Contributions

  • Radiative Transfer Through Complex Stellar Magnetospheres

    Submitted by: Alicia Aarnio
    Authors: Alicia Aarnio, Scott Gregory, Tim Harries, John Monnier (University of North Carolina Greensboro, University of St. Andrews, University of Exeter, University of Michigan)
    In this poster, we present an atlas of spectral line profiles generated via radiative transfer simulations with TORUS (Transfer of Radiation Under Sobolev/Stokes). For T Tauri stars with surface magnetic field maps derived from Zeeman Doppler Imaging (ZDI), we have extrapolated and implemented data-based magnetospheric morphologies and calculate line profiles from a variety of viewing angles, exploring inclination and rotational phase effects. We compare these to line profiles gotten assuming a simple dipolar magnetospheric structure. Finally, we discuss implications for stars with increasingly complex magnetic field morphologies which may not be resolvable by ZDI due to flux cancelation.

  • Reversibility of Turbulent and Non-Collisional Plasmas: Solar Wind

    Submitted by: Belén Acosta
    Authors: Belén Acosta, Denisse Pastén, Pablo Moya (Universidad de Chile)
    We have applied the method known as Horizontal Visibility Graph (HVG) to obtain the Kullback-Leibler Divergence and thus analyze the degree of reversibility of the magnetic fluctuations generated by turbulent plasmas. A particular case of turbulent and non-collisional plasmas is the solar wind. The study of the dissipation of these processes allows us to characterize the behavior of the solar wind and its dynamics in different temporal windows in relation to its magnetic cycles. For this, we have developed the method on simulations Particle In Cell (PIC) for a magnetized plasma, calculating the degree-distance irreversibility parameter for these time-series. Understanding these properties would allow us to characterize the behavior of winds from distant stars.

  • Ab initio formulation of magnetic torques and their influence on the evolution of star-planet systems

    Submitted by: Jérémy Ahuir
    Authors: Jérémy Ahuir (1), Antoine Strugarek (1), Allan-Sacha Brun (1), Stéphane Mathis (1), Emeline Bolmont (1,2), Victor Réville (3) ((1) Laboratoire AIM Paris-Saclay, CEA/Irfu Université Paris Diderot CNRS/INSU, Gif-sur-Yvette, France, (2) Department of Astronomy, University of Geneva, Versoix, Switzerland, (3) UCLA Department of Earth, Planetary and Space Sciences, Los Angeles, CA, Uni)
    Close-in planets can trigger a magnetic interaction with their host star, leading to energy and angular momentum exchange at the origin of planetary migration. The efficiency of this process depends on the magnetic properties of the star and on the characteristics of the planet. We focus here on the case where the planet is not able to sustain a substantial magnetosphere, leading to the so-called unipolar interaction. We use a 3D MHD numerical model of star-planet systems to generate a set of simulations which allows us to explore the parameter space. A simple parametrization of the magnetic torque applied to the planet and of the Poynting flux produced by the interaction is inferred from this grid of models. We then make use of this parametrization of star-planet magnetic interactions in a 1D secular evolution model called ESPEM (French acronym for Planetary Systems Evolution and Magnetism). ESPEM jointly evolves a central rotating star with a bi-layer internal structure, based on the STAREVOL evolution grid, and the semi-major axis of an orbiting planet subject to tidal and magnetic interactions with its host star. By varying important parameters of star-planet systems such as the stellar mass, the initial stellar rotation period, the planetary mass, and the initial semimajor axis, we investigate their role on the evolution of the system and in particular on the fate (destruction or survival) of the planet. We find that for all the systems studied, magnetic and tidal effects both impact the evolution during various phases. In particular, tides have more influence on young systems and magnetism on older systems. Magnetic torques tend to rule the whole evolution for low-mass planets, whereas tidal torques are more effective for high-mass planets. Both effects thus have to be taken into account when predicting the evolution of compact systems.

  • tbd

    Submitted by: Jérémy Ahuir
    Authors:
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  • Simulating Coronal Mass Ejections in Active Stars

    Submitted by: Julián David Alvarado Gómez
    Authors: Julián. D. Alvarado-Gómez (1), Jeremy J. Drake (1), Cecilia Garraffo (2), Sofia P. Moschou (1), Ofer Cohen (3) ((1): Center for Astrophysics | Harvard & Smithsonian, (2) Harvard University, (3) University of Massachusetts at Lowell)
    The stellar magnetic fields completely dominate the environment around late-type stars. They are responsible for driving the coronal high-energy radiation (e.g. EUV/X-rays), the development of stellar winds, and the generation transient events such as flares and coronal mass ejections (CMEs). While considerable progress has been made for the first two processes, our understanding on the eruptive behavior of active stars is still very limited. This information is critical as these phenomena can have a very strong or even catastrophic impact on planetary systems, particularly, during the early stages of evolution where they can become the dominant factor in determining the physical properties around late-type stars. In this context, I will present the results of a numerical project, aimed at studying the properties of eruptive phenomena in active stars. We consider state-of-the-art 3D magneto-hydrodynamic simulations of CMEs in active stars, developed using one of the latest models employed for space weather forecast in the solar system. These results will be discussed in the general solar-stellar context, taking into account the observed properties of the magnetic fields in which they develop.

  • Rotation, magnetic braking and metallicity

    Submitted by: Louis Amard
    Authors: L. Amard & S. Matt (University of Exeter)
    Because of their significant convective envelope, low-mass stars are expected to generate relatively strong, large scale magnetic fields. Coupled to the stellar winds, it leads the star to lose angular momentum and thus to spin down during their entire main sequence lifetime. Various descriptions of that magnetic braking have been developed with different assumptions. With a database of accurate rotation periods larger everyday and a more and more diverse stellar population, it is particularly timely to ask ourselves how different chemical compositions may affect the rotational evolution. I will describe the effect of different chemical composition on the spin evolution of low-mass stars and show how sensitive it can be to metallicity. We also propose to disentangle some of the most recent angular momentum loss description by taking into account the effect of stellar metallicity on the rotational evolution.

  • GPS a novel method to obtain stellar rotational periods: A proxy for estimating faculae to spot surface coverage

    Submitted by: Eliana M. Amazo-Gomez
    Authors: Eliana M. Amazo-Gomez (1,2), Alexander I. Shapiro (1) , Sami K. Solanki (1,4), Natalie A. Krivova(1), Greg Kopp(3), Mahmoudreza Oshagh (2), Timo Reinhold (1), Ansgar Reiners(2) ((1) Max-Planck-Institut fur Sonnensystemforschung, (2) Georg-August Universitaet Goettingen - Institut fur Astrophysik, (3) Laboratory for Atmospheric and Space Physics, (4) School of Space Research, Kyung Hee University)
    The combination of high-precision photometric time-series acquired from Kepler mission, high-stability, high-accuracy measurements of the solar total irradiance (TSI) from SORCE/TIM and SoHO/VIRGO missions, plus the detailed models of solar brightness variations allow better insights into the variability and activity of Sun-like stars. By analysing periodic patterns in observed and simulated light-curves we can link the variability to transits of magnetic features over the stellar surface. We show that the power spectra of simulated brightness variations of stars with magnetic activity similar to that of the Sun and lower do not contain a prominent rotational harmonic. Nevertheless, the rotation periods of those stars can be reliably determined from the profile of the gradient of the power spectra (GPS). We calculate the rotation periods from GPS and compare our results to earlier works based on autocorrelation functions, Lomb-Scargle periodograms, and wavelet maximum peaks. GPS was able to retrieve a rotation period value during seasons of high solar activity when other methods failed. In addition to rotation period were able to determine wether we have facular or spot dominance in the solar surface. GPS shows enhanced manifestations of facular- and spot-related signatures respectively on the third and second power spectra harmonic of the rotation period value. We apply this method to the Sun and to 471 Sun-like stars observed by Kepler, calculate their rotation periods and compare our results to earlier work. The method gives results consistent with others and allows, for first time, the rotation periods of 705 less variable Sun-like Kepler stars to be determined.

  • Impact of stellar magnetism on star-planet tidal interactions

    Submitted by: Aurélie Astoul
    Authors: A. Astoul1, S. Mathis1, C. Baruteau2, F. Gallet3, A. Strugarek1, K. Augustson1, A. S. Brun1, E. Bolmont4 (1AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, France 2IRAP, Observatoire Midi-Pyrénées, Université de Toulouse, France 3Univ. Grenoble Alpes, CNRS, Grenoble, France 4Department of Astronomy, University of Geneva, Switzerland)
    Over the last two decades, about 4000 exoplanets have been discovered around low-mass stars. For the shortest period exoplanets, star-planet tidal interactions are likely to have played a major role in the ultimate orbital evolution and on the spin axis evolution of the host stars. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts the excitation, propagation and dissipation of tidal waves remains open. In this work, we have derived the magnetic contribution to the tidal force and estimated its amplitude all along the structural and rotational evolutions of low-mass stars (from M to F-type). For this purpose, we have used detailed grids of rotating stellar models computed with the stellar evolution code STAREVOL. The amplitude of dynamo-generated magnetic fields is estimated via physical scaling laws at the base and the top of the convective envelope. We find that the star’s magnetic field has little influence on the excitation of tidal waves in near circular and coplanar Hot-Jupiter systems, but that it has a major impact on the waves dissipation. Our results therefore indicate that a full MHD treatment of the propagation and dissipation of tidal waves is needed to assess the impact of star-planet tidal interactions for all low-mass stars along their evolution.

  • Pre-eruptive Magnetic Reconnection within a Multi-flux-rope System in the Solar Corona

    Submitted by: Arun Kumar Awasthi
    Authors: Dr. Arun Kumar Awasthi, Prof. Rui Liu, Prof. Yuming Wang (CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China (USTC), Hefei)
    The core structure of a solar eruption is believed to be a flux rope made of a helical magnetic field. While the post-eruption "standard" picture of the flux rope has been largely studied, the flux rope formation and its evolution toward eruption remain elusive owing to subtle activity and emission during this phase. Here we investigate the pre-eruption morphology of a complex ejecta during the precursor phase of a confined C-class flare exhibiting multiple intermittent brightenings along the polarity inversion line (PIL). Definitive signatures of magnetic reconnection, i.e., nonthermal electrons, flaring plasma, and bidirectional outflowing blobs were evident. Aided by nonlinear force-free field modeling, we conclude that the reconnection occurs within a system of multiple braided flux ropes with different degrees of coherency. The observation signifies the importance of internal structure, pre-eruptive evolution, and dynamics in understanding CMEs and in predicting their impacts on Earth.

  • Asymmetry in Large Scale Plasma Flows and the Sunspot Cycle

    Submitted by: Lekshmi B
    Authors: Lekshmi B, Dibyendu Nandy, H M Antia (1. CESSI, IISER Kolkata, 2. CESSI, IISER Kolkata & Department of Physical Sciences, IISER Kolkata, 3. Tata Institute of Fundamental Research, Mumbai)
    Large-scale plasma flows in the solar convection zone like the differential rotation and meridional circulation play an important role in driving the solar magnetic activity cycle. Understanding these plasma flows and their variations are necessary for getting a better insight of solar magnetic activity and its impact on Earth. The helioseismic observations from Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) are used to study the hemispherical asymmetry in solar torsional oscillation and meridional flow at near-surface layers. We observe that there exist a time-delayed correlation between the asymmetry in the time-varying components of these flows with the magnetic cycle asymmetry, with the plasma flows preceding the sunspot cycle. We speculate that the asymmetry in these large-scale plasma flows can help in predicting the asymmetry in hemispherical magnetic strength. Further, more accurate deep flow measurements over longer time-scales can help in understanding the physical process behind these observed asymmetries and time-delays.

  • Chromospheric activity on low main sequence stars as seen by Galex

    Submitted by: Mauro Barbieri
    Authors: Barbieri Mauro (1), Girardi Leo (2), Dal Tio Piero(3), Zaggia Simone(2) ((1) Universidad de Atacama, (2) INAF OAPD Italy, (3) University of Padua Italy)
    Chromospheric activity increase at decreasing of mass of the stars, due to an increase influence of magnetic fields and large presence of starspots. Here we present the chromospheric activity of low main sequence stars as measured by Galex satellite, and some caveats to distinguish active stars from binary stars with white dwarfs companions.

  • To what degree do regions of open flux located near active regions affect their eruptivity?

    Submitted by: Graham Barnes
    Authors: Graham Barnes (1) and Marc DeRosa (2) ((1) NorthWest Research Associates, Boulder, CO, USA; (2) Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA, USA)
    Most, but not all, large solar flares are associated with coronal mass ejections. The conventional wisdom likely ascribes this association to the large amount of energy released during the flare reconnection process that then becomes available for accelerating matter upward. For those flares that are non-eruptive, what properties set these apart such that there is no discernible eruption? In this study, we investigate whether active regions that produce large non-eruptive flares are correlated with the lack of a nearby channel of open flux in the overlying global coronal magnetic field configuration. We analyze simple models of the coronal magnetic field associated with 56 large flares (in 37 flaring active regions), and evaluate whether properties of the field configuration are associated with the properties of the associated flares. We find a positive association between whether a region is non-eruptive and the absence of nearby open magnetic field lines in the coronal models, however the confidence we assign to this result is limited by the small number of non-eruptive flares in the sample. We also investigate how robust the results of the coronal model are to different ways of constructing the input boundary field.

  • Magnetic properties of lateral downflows in sunspot penumbral filaments

    Submitted by: Luis Bellot Rubio
    Authors: L. Bellot Rubio, S. Esteban Pozuelo, J. de la Cruz Rodríguez (IAA-CSIC, ISP Stockholm University, ISP Stockholm University)
    We have inverted a time sequence of full Stokes spectropolarimetric measurements of a sunspot at the disk center to determine the magnetic properties of the weak downflows that occur at the edges of penumbral filaments. The observations were acquired in the Fe I 6173 line with the CRISP instrument at the Swedish 1m Solar Telescope under superb seeing conditions. They reveal the existence of lateral downflows with unprecedented clarity and allow their temporal evolution to be studied in detail. We find regular two-lobed circular polarization profiles at the position of the downflows. These profiles have small asymmetries and can be inverted sucessfully in terms of one-component magnetic atmospheres with constant parameters along the line of sight. The inversions show that the polarity of the vector magnetic field is usually the same in the downflows and the hosting filament. Sometimes we observe a third weak lobe in the red wing of the circular polarization profile, indicating the presence of opposite polarity fields. This suggests that the downflows drag the field lines but do not change their polarity except on rare occasions. Our results set constraints on the magnetic structure of sunspots that need to be reproduced by 3D MHD simulations.

  • Adaptive Optics at the 1.5m GREGOR Solar Telescope

    Submitted by: Thomas Berkefeld
    Authors: Thomas Berkefeld (Leibniz-Institut für Sonnenphysik)
    We present the adaptive optics (AO) system of the German 1.5m GREGOR solar telescope, Tenerife, which provides diffraction-limited observations in case of good seeing. Each of the three modes of operation has its own correlating Shack-Hartmann wavefront sensors (WFS), allowing to track on extended objects. All modes use the same 256-actuator stacked-piezo deformable mirror (DM) conjugated to the ground. The first mode of operation is the solar on-disk case. Either a single correlation field (conventional AO) or 2x2 correlation fields (ground layer AO) can be used, the former delivering a high Strehl at the center of the field of view, the latter delivering a lower Strehl but more even PSF across a field of up to 12x12 arcseconds. The second mode of operation is the solar prominence AO which uses the H-alpha wavelength for wavefront sensing. For both solar modes the incoming wavefront is sampled with 156 subapertures (91mm subaperture size), yielding up to 140 degrees of freedom for correction of atmospheric turbulence. The third mode of operation is the night-time mode used for polarimetric observations of the solar system planets. We show results and a comparison of corrected and uncorrected observations.

  • Observational study of the dynamics of bright points in a quiet sun region

    Submitted by: Geraldine Berrios Saavedra
    Authors: Geraldine Berrios Saavedra, Santiago Vargas Dominguez (Estudiante maestría astronomía Universidad Nacional de Colombia.)
    High-resolution observations of the solar photosphere are revealing a large of fine structure. Bright Points (BPs) have been identified all over the surface of the sun. In this work, the analysis of BPs is made by using time series of G-band images of the solar photosphere acquired with solar telescopes (e.g. SST, Hinode, Pic du Midi Observatory). Histograms of BPs velocity, and light curves showing their intensity variation, are plotted, and their lifetimes measured, in order to characterize their dynamics and physical properties.

  • Simple Dependence of Proton Density and Temperature on Solar Wind Speed and Compression

    Submitted by: Christopher Bert
    Authors: Christopher Bert, Justin Kasper, Kristopher Klein, Anthony Case, Milan Maksimovic, Arnaud Zaslavsky (University of Michigan, University of Arizona, Smithsonian Astrophysical Observatory, Observatoire de Paris)
    Simple trends between solar wind speed and both temperature and density have long been reported and studied. We show that both are also smooth functions of the radial gradient of solar wind speed (calculated in an Eulerian frame) across many observed timescales, incorporating more than two decades of observations made by the Wind spacecraft. Performing this calculation at a fixed point, as opposed to evaluating the acceleration through space of a particular parcel of plasma, provides a measurement of slope that we use to determine the extent of each parcel’s change in volume due to local stream interaction effects along its propagation through the inner heliosphere. This systematic discrimination between compression (slower wind followed by faster wind) and rarefaction (faster wind followed by slower wind) of all magnitudes forms the basis of a spherical shells model of the solar wind, revealing an adiabatic coupling of temperature and density with change in volume at these scales. It is important to report this as an additional driver of variability in the solar wind, consistent with ideal gas approximations that have been used in literature and models. There is significant potential for this study to inform space environment predictions in preparation for future Parker Solar Probe orbits and other missions, and continued operation at the first Earth-Sun Lagrange point opens the door to simultaneous work with those future experiments.

  • Influence of CME on the gaseous envelopes of hot jupiter exoplanets

    Submitted by: Dmitry Bisikalo
    Authors: Dmitry Bisikalo (Institute of astronomy of the Russian Academy of Sciences)
    The orbital velocities of hot Jupiters, i.e., exoplanets with masses comparable to the mass of Jupiter and orbital semi-major axes less than 0.1 AU, are supersonic relative to the stellar wind, resulting in the formation of a bow shock. Gas dynamic modeling shows that the gaseous envelopes around hot Jupiters can belong to two classes, depending on the position of the head-on collision point. If the collision point is inside the Roche lobe of the planet, the envelopes have the almost spherical shapes of classical atmospheres, slightly distorted by the influence of the star and interactions with the stellar-wind gas; if the collision point is located outside the Roche lobe, outflows from the vicinity of the Lagrangian points L1 and L2 arise, and the envelope becomes substantially asymmetrical. The latter class of objects can also be divided into two types. If the dynamical pressure of the stellar-wind gas is high enough to stop the most powerful outflow from the vicinity of the inner Lagrangian point L1, a closed quasi-spherical envelope with a complex shape forms in the system. If the wind is unable to stop the outflow from L1, an open aspherical envelope forms. In this report we discuss the variations of flow patterns in the gaseous envelopes of hot Jupiters, occurring under the action of coronal mass ejections, by using 3D gas dynamic simulations. We also present the estimates of the variations of atmosphere’s mass-loss rate caused by the influence of typical solar flares and coronal mass ejections.

  • Would the Sun's photosphere be negatively charged ?

    Submitted by: Veronique Bommier
    Authors: V. Bommier (LESIA, Observatoire de Paris)
    No satisfactory solution has been found as yet for the unexpectedly small vertical gradients [with respect to the observed ones] obtained by applying the divB=0 condition [to the solar photosphere magnetic field measurements]" (S. Solanki, 2003, Astron. Astrophys. Rev. 11, p. 184). This is always true today, when an observation review has just been published (H. Balthasar, 2018, Solar Phys. 293, 120). I propose to build an explanation in the frame of the vector law in magnetised media B=µ0(H+M), when the magnetisation M due to the plasma diamagnetism, itself due to the electrons or free charges spiralling about the magnetic field, is large enough. This requires larger than usual model free charges densities in the solar photosphere. However, it can be remarked that inside the Sun, like in the Solar Corona, the electron thermal velocity clearly surpasses their escape velocity. Their charge-dipole interaction with the neutral Hydrogen atoms in the photosphere slow down their escape. They accumulate there and become thus responsible for the non-negligible magnetisation. The last question is to determine if spectropolarimetry measures B or H: I will show that this is H, leading thus to the non-zero observed divergence revealing the presence of a non-negligible magnetisation due to the electrons escaping the Sun's interior.

  • Simulations of ejections of stellar masses and their effects on atmospheres of exoplanets

    Submitted by: Reinaldo Borges Júnior
    Authors: Reinaldo Borges Júnior & Adriana Valio (Universidade Presbiteriana Mackenzie)
    The Sun is a star in relation to an explosive explosion explosion, in which solar explosions and solar winds are a kind of explosive explosion, while solar explosions and solar winds are a kind of explosion. In this tutorial are made computational simulations of the impact of coronal mass ejections on the atmosphere of exoplanets using the code AMUN (Kowal, 2007). From the 90's it was identified that the main source of disturbed solar wind was the giant ejections of matter from the solar corona (Cherenkov and Bisikalo, 2016). These giant ejections are called coronal mass ejections (CMEs) and are characterized as presenting a plasma bubble ejected in the interplanetary medium of approximately 1013 kg, an average energy of approximately 1024 J and speeds ranging from 100 to 3000 km / s, characterizing the movement as supersonic (Zastenker & Zelenyi, 1999; Johnstone et al., 2015, Howard et al., 1985). It is believed that active stars also produce mass ejections. Considering that a CME from a star hits an exopaneta located around it, it will be subject to its action, such as atmospheric erosion, changes in the magnetic field of the exoplanet and the increase of the temperature of the atmosphere, if it exists (Cherenkov and Bisikalo, 2016) . A two-dimensional numerical hydrodynamic (HD) model is used to study, in time and space, structures of CMEs (coronal mass ejections) originating in the stellar crown that propagate through the interplanetary medium. The computational simulations for the accomplishment of such study were done with the code AMUN, entirely written in FORTRAN, developed by Grzegorz Kowal (Kowal, 2007). This code was adapted to simulate the case of a host star and its exoplanet, as well as the study of the influence of mass ejections on the atmosphere of this planet. The ejection of matter is simulated numerically as a pulse of the star's wind, so by imaging it is possible to study the influence of CMEs on the atmosphere of exoplanets. Several parameters were modified, such as stellar wind properties, distance between the exoplanet and the star, planetary radius and composition of the exoplanet atmosphere.

  • Is there a change in magnetic field geometry at the Vaughan Preston gap?

    Submitted by: Sudeshna Boro Saikia
    Authors: S. Boro Saikia, C. Folsom, M. Guedel, S. V. Jeffers, T. Lueftinger, S. C. Marsden, J. Morin, P. Petit, V. See, A. A. Vidotto and the BCool collaboration (University of Vienna)
    The Vaughan-Preston gap is known to divide stars into two separate groups based on their magnetic activity. It suggests two different magnetic field topologies in cool stars operated by two different dynamo processes. We investigate the large-scale geometry of 51 cool stars on either side of the Vaughan-Preston gap. The tomographic inversion technique Zeeman Doppler imaging is applied to reconstruct the stellar large-scale field geometries. Active sun-like stars show field geometries that have both strong surface toroidal and poloidal field unlike the Sun. Inactive stars show a dominant surface poloidal field similar to the Sun. However, no clear separation into a toroidal or poloidal field is seen at the Vaughan-Preston gap. Instead, stellar magnetic field geometries shows a strong correlation with rotation. A sun-like strong poloidal field dominates at Rossby no 1 and greater. One such slowly rotating sun-like star, 61 Cy A, exhibits a magnetic cycle which is similar to the solar case. It is the first and only star to show sun-like magnetic properties. Our results show that instead of an arbitrary separation like the Vaughan-Preston gap, the large-scale magnetic field of sun-like stars can have two different geometries governed by rotation.

  • Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

    Submitted by: Souvik Bose
    Authors: Souvik Bose, Vasco M.J. Henriques, Luc Rouppe van der Voort, Tiago M.D. Pereira (Rosseland Center for Solar Physics, Institute of Theoretical Astrophysics, University of Oslo, Blindern, Norway.)
    The solar chromosphere and the lower transition region is believed to play a crucial role in the heating of the solar corona. Models that describe the upper chromosphere (and lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution (CRD) in the upper chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. We aim to obtain semi-empirical model atmospheres that reproduce the line profiles of the upper chromosphere with focus on a sunspot. We use spectropolarimetric observations of the \ion{Ca}{ii}~8542~\AA\ spectra obtained with the Swedish 1-m Solar Telescope and use NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These are used to synthesize \ion{Mg}{ii}~h\&k spectra using RH1.5D code, which we compare with observations taken with the Interface Region Imaging Spectrograph (IRIS). Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed \ion{Mg}{ii}~h\&k profiles are very well reproduced. In addition, we find that supersonic hot downflows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS \ion{Mg}{ii}~h\&k profiles, with the exception of the line core. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the upper chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot. These are available in electronic and in table formats.

  • The dynamics of solar and stellar activity

    Submitted by: Axel Brandenburg
    Authors: Axel Brandenburg (Nordita, Stockholm)
    Solar and stellar activity reveals itself through chromospheric emission, cyclic variations, and the ejection of helical magnetic fields into the wind. Many young stars exhibit long and short cycles at the same time. Their fields are expected to be predominantly non-axisymmetric, unlike that of the Sun. The point of transition to solar-like behavior is not well reproduced theoretically. There is yet another transition to stars with antisolar differential rotation. Some of the slowly rotating stars in that regime could even exhibit enhanced activity, while others with no significant activity would be unable to brake. The shedding of magnetic helicity is so far only seen for the sun. However, in each hemisphere, the sign of the magnetic helicity in the wind is opposite to that inside the Sun. This is contrary to what was expected if those helicity losses are to alleviate premature quenching. One may speculate that the difficulties of numerical simulations in reproducing solar equatorward migration and differential rotation contours are related to inaccurate modeling of the dynamics of the near-surface shear layer. This layer is characterized by a tremendous change in time and length scales, allowing spontaneous magnetic spot formation in the top-most layers in response to changes in the dynamo-generated field deeper down.

  • The importance of data in understanding gyrochronology models of solar type stars

    Submitted by: Angela Breimann
    Authors: Angela Breimann, Sean Matt, Tim Naylor (University of Exeter)
    Rotation rates of solar-type stars are a key property in understanding their broader stellar evolution, and give an important insight into the physics of stellar magnetic activity and winds. Combined with a spin evolution model, observed rotation rates can also be used to constrain stellar ages, particularly on the main sequence where rotation rates are observed to change on order of approximately a magnitude. Comparatively, other age indicators can struggle during this stage of a star’s lifetime due to barely changing stellar structure. In order to reliably estimate ages, accurate data from large surveys is essential. These data give unprecedented opportunities to constrain masses, radii and luminosities consistently across a variety of clusters, and are therefore crucial to understanding where model assumptions might fail. We present the latest in the development of tools for fitting cluster rotation data to physical models, allowing us to constrain stellar ages and the physics of stellar magnetic activity and winds.

  • Helioseismic insights into the generation and evolution of the Sun’s internal magnetic field

    Submitted by: Anne-Marie Broomhall
    Authors: Anne-Marie Broomhall (University of Warwick)
    Helioseismology uses the Sun’s natural oscillations to probe beneath the Sun’s visible surface, where the Sun’s magnetic field is generated and maintained. The properties of helioseismic acoustic oscillations (p modes) are modified by flows and magnetic fields in the solar interior. Frequencies, amplitudes and damping rates of p modes all vary systematically through the solar cycle, allowing the evolution of the solar interior through a solar cycle to be characterized. Crucially, now, we have a long enough baseline of helioseismic data to perform comparisons of the different activity cycles. In this talk we will review recent efforts to compare and contrast solar activity cycles, from the impact of near-surface magnetic fields on p-mode frequencies to the evolution of the torsional oscillation. We will also discuss the latest attempts to characterize the meridional flows, an important component of many dynamo models. Finally, we will extend the discussion out to other stars, demonstrating how, using helioseismic techniques, asteroseismology can be used to search of evidence of magnetic activity on other stars.

  • The UV/X-ray Radiation and Particle (CME) Fields of M Dwarf Exoplanet Host Stars and How They Evolve

    Submitted by: Alexander Brown
    Authors: Alexander Brown (plus MegaMUSCLES team) (University of Colorado)
    The high energy X-ray and UV radiation fields of host stars play a crucial role in determining the atmospheric conditions and habitability of potentially-habitable exoplanets. Major surveys of the UV/X-ray emissions of M and K type exoplanet hosts are being undertaken by the MUSCLES (125 orbits) and MegaMUSCLES (157 orbits) HST Treasury programs and associated contemporaneous X-ray and ground-based observations. I shall describe the quiescent and flaring radiation (both photons and implied particles) observed from this extensive sample of relatively old, low mass, exoplanet host stars and the resulting implications for planetary habitability. I shall also present results from extensive monitoring campaigns and surveys of X-ray/UV emission from younger M dwarfs and discuss the direct stellar effects that influence exoplanets during the earlier phases of their formation and evolution.

  • Dynamo action in Sun-like stars: What amount of the star's luminosity is accessible?

    Submitted by: Allan Sacha Brun
    Authors: Allan Sacha Brun (1, 2), A. Strugarek (1), K. Augustson (1, 2), J. Varela (1), B. Perri (1), J. Toomre (2) ((1) Department of Astrophysics, CEA Paris-Saclay, France; (2) JILA, University of Colorado, USA)
    We will present a detailed analysis of energy transfers within nonlinear convective stellar dynamos to assess how much of the star's luminosity can be made available through flux emergence to power eruptive events. Based on a series of 15 3-D MHD simulations of solar-like stars spanning 4 bins in rotation and mass we will show what mechanisms are at work and how energy flows from one energy reservoir to another and how global stellar parameters affect the amount of magnetic energy generated by a non-linear stellar dynamo.

  • Study of magnetic field variations in high-cadence vector magnetograms during solar flares

    Submitted by: Willinton Caicedo Tez
    Authors: Willinton Jhomar Caicedo Tez [1] , Santiago Vargas Domínguez [2], Juan Camilo Buitrago [3] (Universidad Nacional de Colombia [1][2], University of California, Berkeley [2])
    Solar flares are an explosive manifestation of the complex magnetic structure of active regions in the solar atmosphere. It has been observed that the photospheric magnetic field of these regions changes rapidly, abruptly and significantly during flaring events. Previous studies are based mainly on visual line or low cadence data. In this work we investigate the temporal and spatial evolution of the permanent changes in the magnetic field of solar flares from high-cadence vector data (135 seconds) of the imaging system (dopplergrams and magnetograms) of the SDO/HMI instrument, which are suitable to probe the phenomenon. The highly energetic events under study occurred during the current solar cycle 24, in a range of high and low energy, according to the GOES classification. The analysis also represents a crucial input for the investigation of sunquakes

  • Magnetoseismology of the Sun

    Submitted by: Paul Cally
    Authors: P. S. Cally (Monash University)
    The absorption of p-modes first observed in the 1980s opened up the possibility of probing helioseismic data for details of the Sun's magnetic fields. Concentrating mostly on local seismology, I will discuss the physics behind both absorption and phase shifts, and implications for the overlying atmosphere. In particular, I will expand on the notion of Magnetoacoustic Portals, introduced by Jefferies et al (2006), to argue that the Sun's interior oscillations cannot be viewed in isolation from the multitude of waves we see in its atmosphere.

  • Emergence of solar active regions as revealed through the analysis of photospheric proper motions

    Submitted by: Jose Ivan Campos Rozo
    Authors: Campos Rozo, J. I., Utz, D., Veronig, A., Vargas-Dominguez, S. (Institute of Physics/IGAM, Karl-Franzens University of Graz; Observatorio Astronomico Nacional, Universidad Nacional de Colombia.)
    The connection and evolution of plasma and magnetic fields in the solar photosphere have been studied before by several authors. The dynamics of features associated to plasma motions as well as magnetic field elements movements can be tracked by using long temporal evolution data and the flow fields associated to such proper motions. In this work we present a detailed analysis showing how the velocity distribution seems to be sensitive to strong changes associated to the emergence of new magnetic elements during the formation of different Active Regions (ARs). The velocities are calculated by using a Local Correlation Tracking (LCT) algorithm applied to continuum maps as well as to Line-of-Sight (LOS) solar magnetograms. We propose two different statistical distributions to fit the velocity magnitude distribution explaining the behavior of the flow fields. The first distribution models the background movements as well as the general proper motions within the field of view, whereas the second component is introduced to obtain information about the fast, and new emergences that appear in region of interest.

  • Magnetic field and prominences of the young, solar-like, ultra-rapid rotator AP 149

    Submitted by: Tianqi Cang
    Authors: T. Cang, P. Petit, J.-F. Donati, C. Folsom (IRAP)
    Young solar analogues reaching the main sequence experience very strong magnetic activity, directly linked to their angular momentum loss through wind and mass ejections. We investigate here the ultra-rapid rotator (P ~ 0.32d) AP 149 in the young open cluster alpha Persei. With a time-series of spectropolarimetric observations gathered over 2 nights in 2006 and 4 nights in 2018, we are able to reconstruct the surface distribution of brightness and magnetic field using the Zeeman-Doppler-Imaging method. Simultaneously, we estimate the short-term brightness evolution through the latitudinal differential rotation. Using the same data set, we also map the spatial distribution of prominences through tomography of H-alpha emission and monitor short-term changes affecting the prominence system. This is the first example of a solar-type star to have its magnetic field and prominences mapped together, which will help to explore the respective role of wind and prominences in angular momentum evolution of the most active stars.

  • The large-scale field of cool and solar-like stars

    Submitted by: Thorsten A. Carroll
    Authors: T. A. Carroll (Leibniz-Institut für Astrophysik Potsdam (AIP))
    What can we extract from the inversion of rotationally modulated Stokes V observations (ZDI) when applied to slow rotating stars? Often a so-called large-scale field is recovered but what is this large-scale field, and what is its relation to the real underlying field, and even more important what is its effect on the polarimetric signal we observe. To shed some light on these questions, we made a number of ZDI inversions of solar-like stars and some illustrative ZDI examples based on synoptic solar magnetograms are shown.

  • Characterizing hot Jupiters via transmission spectroscopy

    Submitted by: P. Wilson Cauley
    Authors: P. Wilson Cauley (University of Colorado Boulder)
    Hot Jupiters are an extraordinary class of exoplanets, orbiting their host stars with periods of hours to a few days. Some of these objects have day-side temperatures approaching photospheric temperatures of late K-type stars. I will give an overview of how we characterize the atmospheres of these fascinating objects and some the more recent exciting results to come from ground and space-based telescopes, as well as what the future holds for detailed characterization of short-period exoplanet atmospheres.

  • Reconstructing solar unsigned magnetograms from Ca II K observations

    Submitted by: theodosios chatzistergos
    Authors: Chatzistergos T. (1,2), Ermolli I. (1), Krivova N.A. (2), Solanki S.K. (2,3), Yeo K.L.(2), Giorgi F. (1) ((1) INAF Ossevratorio Astronomico di Roma, (2)Max Planck institute for Solar system research, (3) School of Space Research, Kyung Hee University)
    Measurements of the solar magnetic field within sunspots date back to 1908, but routine full-disc magnetograms are only available since 1970s. To understand the long-term variability of the Sun (e.g., for dynamo or sun-climate studies), longer series are required. Information about the solar surface magnetism at earlier periods can potentially be recovered from full-disc Ca II K observations. Regular Ca II K observations of the Sun started as early as 1893, thus making the historical Ca II K data a unique source of information on the evolution of plage regions for more than a century. We will present our effort to produce a long-term homogeneous series of unsigned magnetograms from Ca II K observations covering the entire 20th century. We first re-assess the relation between the magnetic flux and Ca II K intensity from analysis of state-of-the-art full-disc and near co-temporal SDO/HMI magnetograms and Rome PSPT Ca II K observations spanning half of the last solar cycle. While all previous such studies were either limited to isolated regions on the solar disc or relied on a very limited sample of observations, we overcome both these limitations. We then apply the derived relation to the recently calibrated data from several historical Ca II K archives to produce unsigned magnetograms covering the period 1893-2018.

  • Effect of viscosity on propagation of MHD waves in astrophysical plasma

    Submitted by: Alemayehu Cherkos
    Authors: Alemayehu Mengesha Cherkos (Addis Ababa University, Institute of Geophysics Space Science and Astronomy)
    We determine the general dispersion relation for the propagation of magnetohydrodynamic (MHD) waves in an astrophysical plasma by considering the effect of viscosity with an anisotropic pressure tensor. Basic MHD equations have been derived and linearized by the method of perturbation to develop the general form of the dispersion relation equation. Our result indicates that an astrophysical plasma with an anisotropic pressure tensor is stable in the presence of viscosity and a strong magnetic field at considerable wavelength.

  • The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

    Submitted by: Georgios Chintzoglou
    Authors: Georgios Chintzoglou, Jie Zhang, Mark C.M. Cheung, Maria Kazachenko (Lockheed Martin Solar & Astrophysics Lab, George Mason University, Lockheed Martin Solar and Astrophysics Lab, University of California Berkeley)
    Active regions (ARs) that exhibit compact polarity inversion lines (PILs) are known to be very flare productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively. We show that such PILs can occur owing to the collision between two emerging flux tubes nested within the same AR. In such multipolar ARs, the flux tubes may emerge simultaneously or sequentially, each initially producing a bipolar magnetic region (BMR) at the surface. During each flux tube's emergence phase, the magnetic polarities can migrate such that opposite polarities belonging to different BMRs collide, resulting in shearing and cancellation of magnetic flux. We name this process "collisional shearing" to emphasize that the shearing and flux cancellation develop owing to the collision. Collisional shearing is a process different from the known concept of flux cancellation occurring between polarities of a single bipole, a process that has been commonly used in many numerical models. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR 11158 and AR 12017, show the continuous cancellation of up to 40% of the unsigned magnetic flux of the smallest BMR, which occurs at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Our results suggest that the quantification of magnetic cancellation driven by collisional shearing needs to be taken into consideration in order to improve the prediction of solar energetic events and space weather.

  • Remote sensing the coronal magnetic field using short radio bursts.

    Submitted by: Brendan Clarke
    Authors: Brendan P. Clarke (1), Diana E. Morosan (1,3), Peter T. Gallagher (1), Vladimir V. Dorovskyy (2), and Alexander A. Konovalenko (2), Eoin P. Carley (1) (Trinity College Dublin (1); Institute of Radio Astronomy of NASU, Kharkov, Ukraine (2); Department of Physics, University of Helsinki, Helsinki, Finland (3).)
    Solar activity is often accompanied by solar radio emission, consisting of numerous types of solar radio bursts. At low frequencies, radio bursts with short durations of milliseconds, such as solar S-bursts, have been identified. To date, their origin and many of their characteristics remain unclear. In this talk, observations from the Ukrainian T-shaped Radio Telescope (UTR-2) and the LOw Frequency ARray (LOFAR) will be presented which give us new insight into their nature. It will be shown that the study of S-bursts and their properties helps us to understand the physics of the coronal plasma and can provide a proxy for measuring the coronal magnetic field. Properties of S-bursts such as duration, drift rate, source velocity and bandwidth were measured. Leading models of S-burst generation were tested for accuracy by analysing the spectral properties of S-bursts. Using various electron density models, S-burst source heights were found to range from ∼1.3-2 R⊙. The coronal magnetic field strengths at the source heights of S-bursts were estimated to range from 0.9-5.8 G. Within error, these values are comparable to those predicted by various relations between magnetic field strength and height in the corona.

  • A large rotational structure around AB Doradus A

    Submitted by: Juan Bautista Climent Oliver
    Authors: Juan B Climent, Rebecca Azulay, Jose C. Guirado (Universitat de Valencia)
    We present high-resolution radio observations of the fast rotating K0V star AB Doradus A. This star was observed with the Australian Long Baseline Array using the VLBI technique at multiple epochs at three different bands (L, X and K). In addition to the well-known compact radio emission associated with the star surface, our maps show a large, rapidly-evolving coronal structure located at 17 stellar radii (0.06 AU). A time series analysis of this coronal component reveals that its motion is nearly coincident with the rotation period of the main star (0.5 d). Although this large structure is most likely produced by the intense magnetic activity of ABDorA, we will report on possible scenarios that might explain its origin, morphology and how it is sustained at such large distances. Possible scenarios include (i) the presence of slingshot prominences, (ii) interaction with an unseen companion, or (iii) a large magnetic loop interacting with a (remanent of) circumstellar disk.

  • Performance and first results with the Integral Field Unit of the GRIS spectrograph at GREGOR

    Submitted by: Manuel Collados
    Authors: M. Collados, C. Dominguez-Tagle, E. Khomenko, N. Vitas (Instituto de Astrofísica de Canarias, Department of Astrophysics of the University of La Laguna)
    Integral Field Units (IFU) have been recently developed and tested at present ground-based telescopes and are key for 2D spectropolarimetry with the 4-m DKIST and EST telescopes. IFUs make possible the simultaneous recording of the full Stokes profiles of spectral lines with high cadence, high spatial resolution and high polarization sensitivity of all points in a 2D field of view. They are thus ideal to understand the complex dynamics and interaction of the solar plasma and magnetic fields, since they can track the evolution of solar features, while measuring at the same time the polarized spectrum. During the last years, the IAC has designed and constructed an IFU based on image slicers and has integrated it with the GRIS spectrograph at GREGOR, the German 1.5-m solar telescope, as a prototype of a future instrument for EST. First-light and commissioning of the instrument was accomplished last September 2018, and the first science campaigns were performed in October 2018. During the commissioning time, a good-seeing quiet-sun temporal series was obtained with a total duration of about 90 minutes and a cadence of 18 seconds, in a field of view of 6"x6". In the series, the granular evolution of granules and magnetic fields is distinct, demonstrating the capabilities of the IFU for capturing an evolving 2D field of view using a spectrograph. During the whole temporal sequence, granules appear, evolve and disappear. Magnetic fields show small-scale patches of different polarity that appear in emerging processes, disappear in submerging processes or when opposite polarity elements approach each other. In this contribution, these phenomena in this data set will be described, and the preliminary results presented and compared to state-of-the-art magnetoconvection simulations.

  • RELATIONSHIP BETWEEN THE VARIATION OF THE X-RAY EMISSION FLOW BY PROXIMA CENTAURI AND THE NUMBER OF RECYCLING MOLECULES OF THE NEXT CEN B ATMOSPHERE

    Submitted by: Paulo Fernando Costa
    Authors: Reinaldo Borges Júnior and Paulo Fernando Costa (Faculdade de Informática e Administração Paulista - FIAP)
    This work presents a discussion about the relation between the X-ray flux variation emited by Proxima Centauri and the number of receiving particles of this radiation in Proxima Cen b. For this, the effective temperature was calculated considering five different albedos (of the terrestrial Moon, of the Earth, Venus, Mars and Uranus), besides obtaining the radiation flux of the star and the radius of the exoplanet. Based on these calculated data, the number of molecules is estimated if the albedo of Proxima Cen b is close of the three presented.

  • Atmospheric Parameters and Ages of M-Dwarfs in the Solar Neighborhood

    Submitted by: Ellen Costa de Almeida
    Authors: de Almeida, Ellen C.*; Porto de Mello, Gustavo F.*; Ubaldo-Melo, Maria L.*;Giribaldi, Riano E.**; Lorenzo-Oliveira, Diego***; Paes-Leme, Nathália M.* (*Valongo Observatory, Federal University of Rio de Janeiro,Rio de Janeiro, RJ, Brazil; **European Southern Observatory, Garching bei München, Germany; ***São Paulo University, IAG, Departamento de Astronomia, São Paulo, SP, Brazil)
    M dwarfs are the most numerous stars in the Galaxy, accounting for more than 70% of nearby stars, making them the most likely hosts of habitable planets [Henry et al 1994, AJ,108, 1437]. They are prime candidates to shelter habitable earthlike planets, as stressed by the recent discoveries of terrestrial exoplanets inside the habitable zones of the nearby M dwarfs Proxima Centauri and Ross 128. Both the transit and radial velocity techniques for detecting exoplanets are much more sensitive to the presence of earth-size planets around M dwarfs than in solar-type dwarfs. Thus the first habitable exoplanet will probably be detected and characterized in a M dwarf environment, making these stars extremely relevant to both astrobiology and planetary science. Even though they are hotspots for the detection of habitable earthlike planets, our knowledge of their properties and even their accurate census stills lags behind with respect to more massive stars. We aim to improve our knowledge of the Teff/[Fe/H] of nearby, still poorly studied M dwarfs, by means of moderate resolution, high S/N NIR spectra, obtained at the coudé spectrograph of the Brazilian 1.6m telescope. We derived a competitive PCA spectral line index calibration able to derive Teff/[Fe/H] with internal errors <100K and <0.1 dex respectively, calibrated against stars with interferometric Teff and [Fe/H] from solar-type binary companions. We present preliminary results for 180 stars, about half of which has no previous Teff/[Fe/H] determination. We also plan to estimate stellar ages by measuring chromospheric fluxes of the Ca II triplet lines, plus an activity-age calibration specifically tailored to M dwarfs derived by our own group [Lorenzo-Oliveira, D. L., 2016, PhD thesis]. Ages for the calibrating M dwarfs were attributed from membership either in moving groups and clusters, binary systems for which the primary star is a solar-type star with known isochronal age, or binary systems in which the primary is a white dwarf with known cooling age.

  • (prelim.) 3D MHD simulations of the wind-wind interactions

    Submitted by: Simon Daley-Yates
    Authors: Simon Daley-Yates (CAE Saclay)
    We present 3D MHD simulations of the wind-wind interactions that occur between a solar-type star and a short period hot Jupiter exoplanet. This is the first such simulation in which the stellar surface evolution is studied in detail. In our simulations a planetary outflow results in the build-up of circumstellar and circumplanetary material which accretes onto the stellar surface in a form of coronal rain. Via a suite of mixed geometry, high resolution simulations, we characterise the behaviour of this wind material for a representative hot Jupiter hosting system. Our results show that magnetic topology plays a central role in forming accretion streams between the star and hot Jupiter. The nature of this accretion is variable in both location and rate, with the final accretion point occurring at 133 degrees west and 53 degrees east of the subplanetary point. The size of the accretion spot itself has been found to vary with a period of 67 ks (approximately 1/5 of the orbital period). Within the accretion spot, there are small perturbations in temperature and density compared with ambient stellar surface conditions. These results are highly dependent on the magnetic fields of both the star and the planet, demonstrating that magnetic fields cannot be ignored in the wind dynamics of star-planet interaction. We characterise this behaviour as Star-Planet-Wind Interaction (SPWI).

  • Stellar rotation, magnetic activity and multifractality in active Kepler stars

    Submitted by: Daniel Brito De Freitas
    Authors: Daniel B. de Freitas (Universidade Federal do Ceará)
    In the present study, we investigate the multifractal nature of time series that were observed by the \textit{Kepler} mission for a sample of 651 stars defined within solar values. Our sample is divided in 130 stars with surface differential rotation traces and 521 stars no differential rotation signature detected. By using the MultiFractal Detrending Moving Average (MFDMA) algorithm, which permits detection of multifractality in nonstationary time series, we estimate possible correlations between the multifractal indices that are based on the singularity spectrum geometrical profile and the relative differential rotation $\alpha$ and absolute horizontal shear $\Delta\Omega$. From the multifractal point of view, the distribution of primary and secondary rotation periods is strongly correlated to the distribution of the Hurst exponent $H$, which is related to a measure of long-term memory of time series. We show that the behavior of distributions of rotation period of stars with and no differential rotation are distinct. Stars with differential rotation detected show a bimodal distribution of rotation period, as well as Hurst exponent one. In contrast, this behavior does not occur for star no differential rotation traces. In addition, our results also emphasize that the parameters $\alpha$ and $\Delta\Omega$ are scaled by the degree of multifractal asymmetry $A$. Another relevant result concerns the fact that the magnetic field of active stars seems to be governed by two mechanisms, characterized by a larger level of complexity on the smaller fluctuations and more noise-like feature of the large fluctuations. Finally, our approach reinforces even more than the stellar rotation is scaled by the presence of different trends in the analysed time series.

  • Solar flares: spectropolarimetric diagnostics

    Submitted by: Jaime de la Cruz Rodriguez
    Authors: Jaime de la Cruz Rodriguez (Stockholm University)
    Solar flares have been studied using theoretical (MHD) and observational approaches. Most of these studies have lately focused in the study of unpolarized radiation in strong chromospheric lines (e.g., Mg II h&k, Halpha, Ca II 8542) or continuum radiation. However, in order to study the role of the magnetic field in flares, polarization must be included in the analysis. Few observational studies have been able to detect and analyze polarization signals in flare observations. In this talk I will review chromospheric diagnostics and aspects of inversion methods that can help taking steps towards better understanding of flare physics from an spectropolarimetric perspective.

  • Models of Evolving Photospheric Magnetic Activity of Sun-Like Stars

    Submitted by: Marc DeRosa
    Authors: Marc DeRosa, Mark Cheung (Lockheed Martin Solar and Astrophysics Laboratory)
    When applied to the solar photosphere, surface-flux transport models have proven helpful toward understanding the effects of various photospheric flow patterns on the resulting magnetic evolution. Evolution on time scales ranging from as short as several days to as long as multiple magnetic cycles has been successfully modeled using these techniques. In the work presented here, we use the surface-flux transport scheme to model the photospheric evolution of magnetic flux on Sun-like stars. With these models, it is then possible to synthesize quantities such as light curves and polarization variations, which may then be used to assess the effectiveness of inversion methods. Alternatively, these models can then be used to drive magnetofrictional models of the coronae of cool stars to provide insight into how stellar coronae might evolve.

  • Effect of Collisions on the Second Solar Spectrum: Recent Advances and New Results.

    Submitted by: Moncef Derouich
    Authors: M. Derouich (ESSTHS, Sousse University, Lamine Abbassi Street, Sousse 4011 H, Tunisia)
    This paper is divided in four parts. In the first part, we intend to review the main recent results on the physics of collisions in the photosphere and the chromosphere of the Sun. Additionally, we draw attention to challenges encountered in the evaluation of the contribution of the collisions for the studies of the second solar spectrum. For instance, we show that it remains a challenge to obtain accurate collisional depolarization rates of the molecular levels. Moreover, it is highly desired to take into account the effect of the magnetic fields and the coherence between the diefferent j-levels (super-coherences) in the calculation of the collisional rates. In the second part, we propose more accurate new determination of the collisional depolarization rate of the upper level of the Sr I 4607 ˚A line by adopting a new interaction potential which is hybrid of the semi-classical RSU potential for long range interatomic distances and quantum ab initio potential at short range distances. This depolarization rate would be useful to accurately interpret the linear polarization of the important Sr I 4607 ˚A line in terms of solar magnetic field. In the third part, we provide general variation laws giving all depolarizing rates due to elastic isotropic collisions required for thestudies of the scattering polarization of neutral and ionized atoms. Finally, in the fourth part, we provide new quantum chemistry results concerning the collisional depolarization rates of the molecular solar lines.

  • High-resolution H-alpha observations of filigree in the vicinity of polar crown filaments and their connection to the magnetic field

    Submitted by: Andrea Diercke
    Authors: Andrea Diercke (1,2), Christoph Kuckein (1), Meetu Verma (1), Carsten Denker (1) ((1) Leibniz-Institut für Astrophysik Potsdam (AIP), (2) Universität Potsdam, Institut für Physik und Astronomie, Germany)
    Polar crown filaments reside at the interface of the more unipolar magnetic fields of the polar caps and the more mixed fields of the active region belts. Mass supply and stability are of concern for all types of filaments but may differ depending on the magnetic field topology and connectivity of the magnetic field supporting the cool plasma in the solar atmosphere. In this study, we focus on chromospheric fine structure on sub-arcsecond scale. A small sample of nine polar crown filaments was observed, while testing a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. In addition to the narrow-band observations with a H-alpha Lyot filter (FWHM = 0.6A), we have broad-band observations with a 7A wide filter centered on the H-alpha line core, in which prominent brightenings are visible, which can be identified as filigree. Restored images of the strictly simultaneous broad- and narrow-band data allow us to connect the location of the filigree to the location of H-alpha fine structure in polar crown filaments. We find that some of the filigree are located close to the footpoints of the polar crown filaments. Furthermore, we analyze the connection of the filigree to the photospheric line-of-sight magnetic field data of the Helioseismic and magnetic imager (HMI) on board the Solar Dynamics Observatory (SDO).

  • Sun-as-a-star Observations of the 2017 August 21 Solar Eclipse

    Submitted by: Ekaterina Dineva
    Authors: E. Dineva [1, 2], C. Denker [1], K. G. Strassmeier [1], I. Ilyin [1], and I. Milic[3] ([1] Leibniz Institute for Astrophysics (AIP), Germany, [2] Institute for Physics and Astronomy, University of Potsdam, Germany, [3] Max-Planck-Institut für Sonnensystemforschung, Germany)
    The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for Large Binocular Telescope (LBT) at Mt. Graham, Arizona. During day-time the instrument is fed with sunlight from the 10-millimeter aperture, fully automated, binocular Solar Disk-Integrated (SDI) telescope. The observed Sun-as-a-star spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength range of 380-910nm. One of the advantages of PEPSI is that solar spectra are recorded in the exactly same manner as nigh-time targets. Thus, we can compare solar and stellar spectra directly. PEPSI/SDI recorded 116 Sun-as-a-star spectra during the 2017 August 21 solar eclipse. The maximum obscuration observed was 61.6%. The spectra were taken with a spectral resolution R≈250000, and an exposure time of 0.3s. The high-spectral resolution enables us to detect subtle changes in the spectra while the Moon passes the solar disk. The Sun-as-a-star spectra are affected by changing contributions due to limb darkening and the solar differential rotation profile, and to a lesser extend by the presence of active regions on the solar surface. We investigate the temporal evolution of the chromospheric Na D1 and D2 lines, derive bisector yielding height-dependent information, and compare observations with synthetic line profiles computed with the state-of-the-art Bifrost code.

  • The Solar & Stellar Flare Connection

    Submitted by: Lauren Doyle
    Authors: L. Doyle, G. Ramsay, J. G. Doyle, E. Scullion (Armagh Observatory and Planetarium, Northumbria University)
    We have high cadence, Halpha observations of a filament eruption made using the CRISP spectro polarimeter mounted on the Swedish Solar Telescopes. These data have allowed us to determine 3D velocity maps of the event. To gain insight to the physical mechanism which drives the event we have modified an existing 3D MHD reconnection model to simulate the observations. Although there is no direct relation between solar type stars and fully convective stars, this work may illuminate our K2 observations of low mass stars. After spectral type M4 stars become fully convective and do not generate a magnetic field in the same was as the Sun. These stars are highly active producing flares with energies up to 1034 ergs and can show many flares. However, surprisingly there is no correlation between the number of flares and the rotation cycle, since we would expect more flares at flux minimum when the starspot is most visible. Despite their fully convective nature, our solar model can be used to aid our understanding of the origin of flares in low mass stars. We outline three scenarios to explain our finding: polar spots, stellar binarity systems and the presence of orbiting planets. By scaling up our solar model to replicate flare energies seen in the stellar flares we aim to investigate these scenarios. We will determine the energy of the flare as a function of distance between footpoints, velocity and magnetic energy. The links between the stellar scenarios and solar model can be used to influence future models on fully convective stars.

  • New limit on ∆α/α over cosmological scales

    Submitted by: Le Duc Thong
    Authors: Le TD (Institute for Computational Science)
    A new limit on the space-time variation of the fine-structure constant (α= e^2/(4πε_0 ℏc)) was found from an analysis of Mg II line from quasar J110325-264515 with redshift z_abs=1.8389. The obtained result is ∆α/α=(-0.155±0.728)×〖10〗^(-6) by a comparison of the Mg II line seen in J110325-26415 quasar spectra with those found in the laboratory. This result provides us an important tool to check the possibilities of space-time variations in the fine-structure constant and can improve this limit in the future.

  • Diagnostics of non-thermal distributions from solar flare EUV line spectra

    Submitted by: Elena Dzifčáková
    Authors: Elena Dzifcakova (1), Jaroslav Dudik (1), Alena Zemanova (1), Luraj Lorincik (1), Vanessa Polito (2) ((1) Astronomical Institute of the Czech Academy of Sciences Fricova 298, Ondrejov, Czech Republic)
    Solar flares are the most energetic manifestations of the solar magnetic activity. The presence of the high-energy electrons accelerated by magnetic reconnection during solar flares affect X-ray and also EUV emission spectra. Recent theoretical papers and RHESSI observations of coronal X-ray sources suggested that the electron distribution function could have a form of kappa-distributions. Using KAPPA package based on the CHIANTI database, synthetic SDO/EVE (Extreme Ultraviolet Variability Experiment) spectra for different temperatures, electron densities and parameter kappa were calculated and utilized to propose diagnostics of the plasma parameters. The diagnostics based on the spectral line intensity ratios were applied on the Fe flare line intensities in the SDO/EVE spectra observed during strong flares. We show that kappa-distributions have only a small effect on the diagnosed electron densities but they strongly influence temperatures diagnosed from the line ratios involving different ionization degrees. Diagnostics of the distribution function from relative line intensities demonstrated the presence of the strongly non-thermal distribution during the impulsive phase of the flare and later gradual thermalization of the electron distribution. Beside electron distribution, the ion distributions also show signatures of presence of non-thermal distributions. The line profiles of high-temperature Fe XXIV lines observed by the Hinode/EIS Extreme-Ultraviolet Imaging Spectrometer (EIS) during the impulsive phase of flare show broad profiles with pronounced wings and can be well fitted by a strongly non-thermal kappa-distribution. We discuss the coincidence of the location of high-energy hard X-ray (HXR) sources observed by RHESSI and their parameters with the regions with non-Gaussian profiles and with the effects of the non-thermal electron distribution in the EUV line spectra.

  • On the multi fractality of plasma turbulence in the solar wind.

    Submitted by: Sebastian Echeverrua
    Authors: Sebastian Echeverria, Pablo Moya, Denisse Pasten (Universidad de Chile)
    The upper atmosphere of the sun, the corona, is continuously releasing a stream of charged particles which constitutes the solar wind. This ejected plasma gives an extent of interesting phenomena in plasma physics. One of the fundamentals problems in this area is the understanding of the relaxation process in a collisionless plasma and the resultant state of the electromagnetic turbulence, in particular at kinetic scale. In this work, considering numerical Particle-In-Cell simulations we apply a method known as MultiFractal Detrended Fluctation Analysis (MFDFA) to study the magnetic fluctuations of plasmas in thermodynamic equilibrium (represented by Maxwells velocity distribution functions), and out equilibrium plasmas represented by Tsallis distribution functions, characterized by a the κ (kappa) parameter related with power-law tails at higher energies. In particular, where explore the relation between the multifractality of magnetic fluctuations time series, extracted from the simulations, and the kappa parameter. Our results can led to a new tool to characterize the electromagnetic turbulence, and its dependence on the plasma parameters, in collisionless space plasmas such as the solar wind. Furthermore, this tool could be useful to extract valuable information about the plasma when high resolution particle detectors are not available.

  • Solar wind driven instabilities at kinetic scale

    Submitted by: Zahida Ehsan
    Authors: Z. Ehsan (COMSATS University Islamabad, Lahore Campus)
    Studying fundamental plasma processes such as waves and instabilities; excitation and damping mechanism is also important for understanding the Sun and the stars, predicting space weather and understanding the plasma behavior in laboratory devices as well. But there is a lot to be explored. In plasmas with an electron drift current relative to static ions, ion acoustic waves are subject to the kinetic instability. The instability threshold however, when one quasi- neutral electron-ion plasma propagates through another static target plasma, may be well below the ion acoustic speed of the static plasma. Such a currentless instability may frequently be driven by the solar wind when it permeates through another plasma in space. Such kinetic instabilities were previously studied in the framework of thermodynamically stable plasmas obeying a Maxwellian behavior. Recently, it has become possible to construct the distribution function from the empirical data, which is found to deviate from the Maxwellian due to the presence of high energy tails and shoulders in the profile of the distribution functions. Using Boltzmann-Vlasov kinetic model with the flat-top non-Maxwellian distributed electron –ion, a velocity power law energetic tail, known as the generalized (r, q) distribution, a currentless electrostatic instability namely ion acoustic which is driven by a stream of solar wind plasma is studied here. The instability threshold is affected and depends upon the spectral indices r and q. It is found that the growth rate increases with the decrease in the value of r and increase in q. As a special case, we also discuss the presence of interstellar dust and discuss dispersion properties and growth rates of ion/dust acoustic modes quantitatively.

  • Shock wave propagation through the solar chromosphere

    Submitted by: Henrik Eklund
    Authors: Henrik Eklund, Sven Wedemeyer, Mats Carlsson (Rosseland Centre for Solar physics, Institute of theoretical astrophysics)
    High cadence time series from solar ALMA observations are used to study shock wave propagation through the solar chromosphere. This gives a tool to understand the small scale structure, complex dynamics and heat transfer in the chromosphere. In addition an idealised case with waves excited in one dimensional atmospheres from RADYN is used along with Bifrost simulations. The latter gives a more realistic environment with interfering and merging shock waves. Together they give a qualified picture and valuable indications of how to find shock waves in the observational data. Variations of the (continuum) brightness temperature across the ALMA receiver bands provide spectral signatures that allow to investigate the properties of shock waves and their propagation through the chromosphere. The simulations show several seconds delay of the shock wave signatures between the outermost receiver bands, which agrees with the observational ALMA time series with a cadence of two seconds. In addition, these results can be used as an aid in determining the radiative formation height of the ALMA receiver bands.

  • The various scenarios for the equatorward migration of sunspots

    Submitted by: Detlef Elstner
    Authors: Detlef Elstner, Yori Fournier, Rainer Arlt (Leibniz-Institut für Astrophysik Potsdam (AIP))
    The profile of the differential rotation together with the sign of the alpha-effect determine the dynamo wave direction. In early models the dynamo wave often lead to a poleward migration of the activity belts. Flux transport by the meridional flow or the effect of the surface shear layer are possible solutions for the problem. Beside the influence of meridional flow the role of boundaries on the properties of mean field dynamos is discussed. Finally we present a new dynamo of Babcock-Leighton type, which leads to the correct equatorward migration by the non-linear relation between flux density and rise time.

  • Solar Astrometry with Planet Transits

    Submitted by: Marcelo Emilio
    Authors: Marcelo Emilio, Jeff Kuhn, Rock Bush, Isabelle Scholl (Universidade Estadual de Ponta Grossa, University of Hawaii, Stanford University, University of Hawaii)
    Planetary transits are used to measure the solar radius since the beginning of the 18th century and are the most accurate direct method to measure potentially long-term variation in the solar size. Historical measures present a range of values dominated by systematic errors from different instruments and observers. Atmospheric seeing and black drop effect contribute as error sources for the precise timing of the planetary transit of ground observations. Both Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO) made observations of planetary transits from space to derive the solar radius. This work details the solar size determined during the planetary transits of Venus in June 2012 and of Mercury on 2003 May 7 and 2006 November 8. The International Astronomical Union approved the resolution B3 in 2015, defining a nominal solar radius to be precisely 695,700 km. In this work, we show that this value is off by more than 200 km that is one order of magnitude higher than the error of our observations.

  • Characterization of stellar activity using transits and its impact on habitability

    Submitted by: Raissa Estrela
    Authors: Raissa Estrela (Jet Propulsion Laboratory/Caltech, Center for Radioastronomy and astrophysics Mackenzie (CRAAM))
    Stellar magnetic field is the driver of activity in stars and can trigger spots, energetic flares, coronal plasma ejections and ionized winds. These phenomena play a crucial role in understanding the internal mechanisms of the star, but can also have potential effects in orbiting planets. During the transit of a planet, spots can be occulted producing features imprinted in the transit light curve. Here, we modelled these features to characterize the physical properties of the spots (radius, intensity, and location). In addition, we monitor spots signatures on multiple transits to estimate magnetic cycles length of Kepler stars. Flares have also been observed during transits in active stars. We derive the properties of the flares and analyse their UV impact on possible living organisms in planets orbiting in the habitable zone.

  • Transition to Chaos and Hyperchaos in Magnetoconvection

    Submitted by: Francis Ferreira Franco
    Authors: F. F. Franco¹; E. L. Rempel², P. Muñoz² ([1] Aeronautics Institute of Technology; [2])
    Cosmic magnetic fields are generally associated with turbulent motions, which can be driven by thermal convection. The Rayleigh-Bénard convection is an idealized version of thermal convection and it has been often employed to understand instabilities, chaos and atmospheric turbulence. Magnetoconvection is the study of the interaction between thermal convection and magnetic fields when a background field is imposed, and its original motivation was the understanding of the dynamics of magnetic fields in the solar photosphere. In this work, a numerical study of a reduced model of magnetoconvection is presented. By considering a horizontal background magnetic field in a conducting fluid in a plane layer, a generalized Lorenz model is derived and used to investigate transitions to chaos and hyperchaos as a function of two control parameters, the reduced Rayleigh number and the magnitude of the background magnetic field. The power spectra and the spectrum of Lyapunov exponents are used to describe the system states. As a result, a hyperchaotic saddle is found and a new transition from quasi-periodicity to hyperchaos is presented.

  • Characterization and dynamics of small scale Moving Magnetic Features (MMF) around a solar pore.

    Submitted by: Anyul Steak Figueroa Moya
    Authors: Anyul Figueroa Moya, Santiago Vargas Domínguez (National University of Colombia)
    The most notable phenomenon of active regions in the Sun are sunspots and pores. Around pores (sunspots without penumbra), bright structures that move away radially (called Moving Magnetic Features or MMFs) have been observed. When appearing around a pore, MMFs are found to be either unipolar (positive or negative magnetic field) or bipolar (pairs of magnetic fields) and having an average sizes of less than one arcsecond. Making use of images acquired with ground-based solar telescopes (e.g. Solar Swedish Telescope, SST) and space-borne telescopes (e.g. SDO), the dynamics of MMFs is characterized by using a tracking algorithm in sequences of filtergrams. Physical properties such as their displacements, lifetimes, velocity and intensity, are analyzed in this work.

  • Solar and Stellar Rotation - Current Developments in Wind Braking

    Submitted by: Adam Finley
    Authors: Adam J. Finley, Sean P. Matt & Victor See (University of Exeter)
    The rotational evolution of low mass stars (<1.3 Solar Mass) is governed by stellar winds which slow the stellar rotation during their main sequence lifetimes. The interaction of their global stellar magnetic field increases the effectiveness of this braking process. To model this, I compute a grid of MHD simulations with a range of stellar wind parameters and magnetic topologies. Using this grid of models I fit semi-analytic relationships capable of accounting for complex magnetic geometries, which are generally applicable in rotational evolution calculations. To develop these models further, I have taken advantage of the wealth of solar data available from in-situ and remote-sensing and applied the formulae to estimate the current solar wind braking. The Sun has a variable magnetic field with times of high complexity and others of simple dipolar configuration. This variability is shown to effect the braking rate, and with magnetic variability commonly observed in other Sun-like stars, I also discuss the implications for applying the formula to other Sun-like stars where the magnetic variations are ill-constrained. Through the use of Zeeman-Doppler imaged stars I examine the effect of their magnetic variability and compare these to the rotational evolution models.

  • The Variable Nature of Angular Momentum Loss from Low-Mass Stars

    Submitted by: Adam Finley
    Authors: Adam Finley (U. of Exeter, Dept. of Physics & Astronomy)
    The rotation period evolution of low-mass stars (<1.3 Solar Mass) is governed by their stellar winds, which remove angular momentum during the main sequence. Their dynamo-driven magnetic fields play an important role in governing the effectiveness of the braking torque. To better understand this, we use MHD simulations to model the stellar winds of low-mass stars. By using a range of wind parameters and magnetic topologies, we derive semi-analytic relationships capable of reproducing the braking torque on a star, based on its surface magnetic field strength. To develop these further, we take advantage of the wealth of solar data available from in-situ and remote-sensing, and apply our formulae to estimate the current solar wind braking torque. The Sun has a variable large-scale magnetic field, which we show to affect the braking torque on the Sun, due to the solar wind. We also apply our braking formula to other Sun-like stars, by using results from Zeeman-Doppler imaging. We calculate the time-varying torque due to the observed magnetic variability of four Sun-like stars, and compare these torques to those produced by modelling the rotation period evolution of low-mass stars. We find that our stellar wind torques are systematically lower than those from rotation evolution models. Stellar wind variability appears unable to resolve this discrepancy, implying that there remains some fundamental issues with current stellar wind models which have yet to be understood.

  • Dispersion properties and stability of Kinetic Alfvén Waves in the Earth’s Magnethosphere

    Submitted by: iván gallo
    Authors: Iván Gallo, Pablo S. Moya, Beatriz Zenteno. (Departamento de física de la Universidad de Chile)
    Kinetic Alfv\'en Waves (KAWs) are a mode of propagation of plasma waves, which propagate oblique respect to the background magnetic field, and have frequencies in the range of the proton cyclotron frequency. One of the most important properties of these waves is that KAWs have a right-handed polarization in the plasma frame. Thus, wave-particle interactions with KAWs tend to be non-resonant with ions and resonant with electrons. In fact, these waves are considerate as a possible channel to transfer energy to small electron scales, being of particular interest to the space plasma physics community. We study the dispersion properties of Kinetic Alfvén Waves in multi-species plasmas composed by electrons, protons, and O+, with macroscopic plasma parameters relevant to the inner magnetosphere environment. We use Vlasov linear theory to find the dispersion relation and study the growth/damping rates and polarization of the waves, considering different concentrations of the O+ ions, which may be relevant especially during geomagnetic storms

  • How does the vertical magnetic field drive the formation of starspots? -The solar case.

    Submitted by: Marta García Rivas
    Authors: Jurčák, J. (1), García Rivas, M. (1) & Bello González, N. (2) ((1) Astronomical Institute of the Czech Academy of Sciences. (2) Kiepenheuer Institut für sonnenphysik)
    Most of the stars, where starspots were detected, are so distant that it is yet impossible to spatially resolve them. However, we can find a star that can be spatially resolved: the Sun. In some cases, the study of the Sun allow us extrapolate its properties to other stars. In this talk we will review the research that signifies the importance of the vertical component of the magnetic field to inhibit convective motions and thus create umbrae on the solar surface. The discovery of a constant vertical magnetic field on the boundary between umbra and penumbra in sunspots (Jurčák, J. 2011) triggered further research of sunspots and other magnetic structures, such as pores. Statistical analysis led to the Jurčák's criterion. This criterion states that the boundary between the umbra and the penumbra in a stable sunspot is characterized by a constant vertical magnetic field meaning that, when the vertical magnetic field is stronger than a critical value, the umbral convection mode occurs. However, magnetic structures with the vertical magnetic field weaker than such critical value are unstable against more vigorous modes of magnetoconvection and prone to vanish. We want to present the Jurčák's criterion to the stellar community to ponder its implications and importance for starpots.

  • Curve of the space-time tissue and its relation to the size of different bodies

    Submitted by: Leonardo Goncalez
    Authors: Leonardo Gomes Jorge Gonçalez (Faculdade de Informática e Administração Paulista - FIAP)
    Based on general relativity, it is known that bodies with mass and energy can bend the tissue of space time and thus generate the gravitational field. With this in mind, the article will analyze how the intensity of the curve reacts taking into account bodies with the same mass and energy, but with different sizes. Taking the example of the black holes that were previously supernovae, when reducing to the size of a grain of rice because they intensify their gravitational force where nor point of the light can not escape? Does your radius change? The research will take all of this into account to answer a question that may be simple but that can help take a step to understanding how the universe works and how it can help us.

  • What do open clusters tell us about the evolution of the Sun’s magnetic activity?

    Submitted by: Philippe Gondoin
    Authors: P. Gondoin (European Space Agency)
    Characterizing the long-term evolution of magnetic activity on the Sun and Sun-like stars is important not only for stellar physics but also for understanding the environment in which planets evolve. In the past decades, many surveys of open clusters have produced extensive measurements of rotation periods, lithium abundances, and activity indices on stars of different ages. I combine these data to infer a long-term evolution scenario of magnetic activity on Sun-like stars. The derived scenario uncovers unexpected features of their rotation-activity relationship, angular momentum evolution, and rotation rates distributions in open clusters.

  • Chromospheric magnetograms as lower boundary for nonlinear force-free field extrapolations of solar magnetic field in the corona.

    Submitted by: Sanjay Gosain
    Authors: Sanjay Gosain (National Solar Observatory)
    It is known that the magnetic field in the dense turbulent photospheric layers is far from force-free equilibrium. For reliable coronal magnetic field extrapolations using non-linear force-free field (NLFFF) extrapolation procedures it is mandatory that lower boundary should be in force-free equilibrium. In fact, many NLFFF procedures try to artificially reduce net Lorentz forces in the photospheric vector magnetograms by first processing them before using in extrapolation. It is believed that magnetic field in the chromosphere is more close to force-free equilibrium than in photosphere. We will use SOLIS/VSM chromospheric vector field measurements of active regions, obtained in Ca II 854.2nm spectral line to (i) verify that the force-free equilibrium condition, and (ii) NLFFF extrapolations, both are better than with photospheric vector magnetograms. The correct reconstruction of coronal magnetic field has a huge impact on estimates of magnetic free-energy and helicity content of solar active regions, both released in solar flares and coronal mass ejections (CMEs).

  • Observational constraints of solar-like stellar winds

    Submitted by: Manuel Guedel
    Authors: Manuel Guedel (University of Vienna)
    Ionized and magnetized winds are important for the spin-down of late-type main-sequence stars, therefore controlling the long-term evolution of stellar magnetic activity. The latter is a key factor in driving the evolution of planetary atmospheres and, for certain planets, the emergence of habitable surface conditions. Wind-related star-planet interactions include coronal mass ejections, but also steady interactions with upper planetary atmospheres (e.g., charge exchange reactions, ion pickup, sputtering) that may lead to atmospheric erosion through non-thermal loss processes. Detecting stellar winds is challenging. I will discuss several methods including direct detection of wind bremsstrahlung and attenuation, charge exchange, and indirect inferences from stellar spin-down, planetary atmospheric loss, or Ly alpha absorption. I will discuss present constraints of stellar winds and their evolution from relevant observations.

  • Global numerical MHD simulations

    Submitted by: Gustavo Guerrero
    Authors: G. Guerrero, P. Smolarkiewicz, A. Kosovichev, E. M. de Gouveia Dal Pino, A. Bonanno (UFMG, ECMWF, NJIT, IAG-USP, OAC-INAF)
    New high quality results from stellar observations have allowed to measure and characterize magnetic fields in stars of almost all types. The results indicate that the magnitude, morphology and temporal evolution of the magnetic fields differ depending on the mass, evolutionary stage and the rotation of the stars, indicating that they may have a different origin. In this talk I will present recent results of global MHD dynamo simulations of stars of different types across the HR diagram performed with the EULAG-MHD code. The aim of these simulations is to determine the mechanism generating and sustaining the magnetic field in objects including T Tauri, solar-like and Ap/Bp stars. An important result from the simulations regards to the role of radial shear layers, located at the interface between radiative and convective zones, on the generation process. In T Tauri objects its presence determines the morphology of the magnetic field. In solar-like stars, the generation of the field in this layers leads to magnetic cycle periods in agreement with the observations. The role of MHD instabilities to amplify and sustain magnetic fields in radiative layers will also be discussed.

  • Dynamics of solar isolated features observed by the Atacama Large Millimeter/submillimeter Array (ALMA).

    Submitted by: Juan Camilo Guevara Gomez
    Authors: Guevara Gomez J.C., Jafarzadeh S., Szydlarski M., Wedemeyer S. (Rosseland Centre for Solar Physics, Institute of Theoretical Astrophysics, University of Oslo)
    Four time series of solar images, observed by the Atacama Large Millimeter/submillimeter Array (ALMA) in December 2016 and in April 2017, were analysed. The datasets were recorded in bands 3 and 6 at 2.6-3.6 mm and 1.1-1.4 mm, respectively. This study focused on the tracking of isolated solar features, including both bright and dark small-scale structures. Tracing structures in image time series yields information about their lifetimes, velocities, and area variation with time. Observations with the Solar Dynamics Observatory (SDO), which have been co-aligned with the ALMA images, provide context in particular regarding the large-scale structures at various layers of the solar atmosphere and complement the analysis of the tracked features.

  • Impact of small-scale emerging flux from the photosphere to the corona: a case study from IRIS

    Submitted by: Salvo Guglielmino
    Authors: Guglielmino, S. L.(1); Young, P. R.(2); Zuccarello, F.(1); Romano, P.(3); Murabito, M.(4) ((1) Università degli Studi di Catania - Catania, Italy; (2) Code 671, NASA Goddard Space Flight Center - Greenbelt, MD, USA; (3) INAF Catania Astrophysical Observatory - Catania, Italy; (4) INAF Astronomical Observatory of Rome - Rome, Italy)
    Magnetic flux can emerge into the solar atmosphere in various magnetized environments, giving rise to eruptive phenomena owing to the interactions between new and pre-existing fields. This certainly occurs on large scales, eventually triggering flares and CMEs. However, also at small scale the appearance of an emerging flux region (EFR) in the photosphere may have a far-reaching impact up to the corona. Here, we report on multi-wavelength ultraviolet (UV) high-resolution observations taken with the IRIS satellite during the emergence phase of an EFR embedded in the unipolar plage of active region NOAA 12529. These data are complemented by measurements taken with the spectropolarimeter aboard the Hinode satellite and by full-disk observations from SDO. In the photosphere, magnetic flux emergence is recognized in the appearance of opposite emerging polarities, separating from each other, and in the fuzzy granulation in the region between the emerging polarities, which is also characterized by nearly horizontal fields. During flux emergence, a pre-existing photospheric flux concentration of the plage is seen cancelling with the opposite polarity flux patch of the EFR. In the upper atmospheric layers, recurrent brightenings resembling UV bursts, with counterparts in all UV/EUV filtergrams, are identified in the EFR site. An arch filament system (AFS) overlies the EFR in the chromosphere. Plasma ejections are also found at chromospheric and coronal levels, above the AFS and near the observed brightness enhancement sites. The analysis of the IRIS line profiles in the bursts reveals spectral features indicating the heating of dense plasma in the low solar atmosphere and the driving of bi-directional high-velocity flows, with speeds up to 100 km/s. Most important, we unravel a signature of plasma heated up to 1 MK in the core of the brightening sites, as indicated by Fe XII emission. Comparing these findings with previous observations and numerical models, we suggest evidence of several long-lasting, small-scale magnetic reconnection episodes between the new bipolar EFR and the ambient field. This process, leading to flux cancellation, appears to occur higher in the atmosphere than usually found in UV bursts, being responsible for heating and plasma ejections that involve all the atmospheric levels.

  • Ellerman bombs and UV bursts: Flux emergence and reconnection at different atmospheric layers?

    Submitted by: Viggo Hansteen
    Authors: Viggo Hansteen (Rosseland Centre for Solar Physics, Lockheed Martin Solar and Astrophysics Laboratory)
    Three-dimensional (3D) Magnetohydrodynamic (MHD) “realistic” models of the solar chromosphere and lower corona have now progressed to the point where meaningful comparisons of synthetic observables and solar data can be made. The emergence of magnetic flux through the photosphere and into the outer solar atmosphere produces, amongst many other phenomena, the appearance of Ellerman bombs (EBs) in the photosphere. EBs are observed in the wings of H(alpha) and are highly likely to be due to reconnection in the photosphere, below the chromospheric canopy. But signs of the reconnection process are also observed in several other spectral lines, typical of the chromosphere or transition region. An example are the UV bursts observed in the chromosphere in lines of Ca II and Mg II and transition region lines of Si IV. In this work we compare the diagnostic signatures made by numerical models of such reconnection events with high cadence coordinated observations between the 1-m Swedish Solar Telescope and the IRIS spacecraft. We see no compelling reason to posit that UV bursts occur in the photosphere. Rather, we propose that the observations point to a scenario where the chromosphere has become vastly bloated with slowly rising (10 km/s) cool fairly dense gas, up to 10 Mm or more. Further that this cool gas supplies the necessary opacity to explain absorption in cool lines such as from Ni II and Mn I, and in the continua of hydrogen and neutral and singly ionized helium. These providing narrow absorption bands in the Si IV and Mg II line wings, and continuum absorption suppressing the evidence for intense heating in the AIA bands such as 30.3, 17.1, and 19.3 nm in the lower regions of the expanded active region chromosphere.

  • Spectropolarimetry with 854.2 nm compared with ALMA and scattering polarization theory

    Submitted by: John Harvey
    Authors: J. W. Harvey (National Solar Observatory)
    Regular spectropolarimetric observations of the Sun are made by the National Solar Observatory using the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectromagnetograph (VSM). Among these observations are full Stokes spectra using the 854.2 nm Ca II line. Nearly simultaneous images are compared with ALMA 100 and 239 GHz solar images. Intensity images made near the core of the Ca II line agree quite well with the ALMA brightness images, suggesting that the signals arise from roughly the same heights. With polarimetric sensitivity close to 1E-4 the core of the Ca II line shows dynamic linear polarization features over most of the solar disk. The linear polarization appears to be closely associated with elongated fibril structures. These observations are compared with theoretical predictions and found to be in good agreement. This polarization puts severe limits on the ability to measure vector magnetic fields in the chromosphere using the Zeeman effect of Ca II 854.2 nm.

  • TESS light curves of low-mass eclipsing binaries

    Submitted by: Krzysztof Helminiak
    Authors: K. Helminiak (NCAC Torun, Poland)
    We present high-precision light curves of several M- and K-type, active eclipsing binaries, recorded with 2-minute cadence by the Transiting Exoplanet Survey Satellite (TESS). Analysis of these curves, combined with radial velocity data, allows to vastly improve the accuracy and precision of stellar parameters with respect to previous studies of these systems.

  • The Magnetic Activity of Proxima Centauri star during 2017-2018

    Submitted by: Gabriel Hickel
    Authors: Hickel, G.R.(1); Barbosa, L.R.(1); Feitoza, N.N.R.(1); Mota, A.(2); Maia, A.(2); Ribeiro, D.(2); Carolino, R.(2); Carvalho, T.(2) ((1) Universidade Federal de Itajubá (UNIFEI) ; (2) Instituto Federal do Rio de Janeiro (IFRJ))
    Proxima Centauri is the red dwarf star M5.5V and also the closest to the Solar System. It is probably part of a triple system, also composed by Alpha Centauri A and B. The importance of this star grew from this year 2016, with the discovery of a possible planet orbiting around it, with mass similar to of Earth and apparently within the so called "habitable zone". Despite being one of the few red dwarfs close enough to determine more detailed studies of surface magnetic activity, long-term monitoring of Proxima Centauri is practically non-existent in the literature. Like a red dwarf star, its internal structure is almost completely convective, leading to intense and complex magnetic activity on its surface, with intense flares. In 2017, we started a monitoring program of the Proxima Centauri´s magnetic activity, observing the H-alpha line (6563 Å), using a LHIRES-III spectrograph coupled to the Zeiss telescope at the Pico dos Dias Observatory (Brazil). In this work, we present the results of the first two years, including large flares detected and the statistic of activity states.

  • Relating the Structure and Dynamics of the Corona to the Variability of the Solar Wind

    Submitted by: Aleida Higginson
    Authors: Aleida K. Higginson; Spiro K. Antiochos; C. Richard DeVore (JHU/APL ; NASA Goddard Space Flight Center; NASA Goddard Space Flight Center)
    Recent coronagraph and in situ observations have shown that the slow solar wind includes highly structured and dynamic outflow across spatial scales, most likely due to magnetic reconnection processes in the solar corona. In the age of Parker Solar Probe and the forthcoming Solar Orbiter mission, understanding this temporal and spatial variability has become essential. Numerical calculations have shown that magnetic field dynamics at coronal hole boundaries, in particular interchange reconnection driven by photospheric motions, can be responsible for the dynamic release of structured slow solar wind, including along huge separatrix-web (S-Web) arcs formed by pseudostreamers. Quantifying the solar wind variability along these S-Web arcs is crucial to furthering our understanding of how coronal magnetic field dynamics can influence the plasma and magnetic field throughout the heliosphere. Here we present for the first time, fully dynamic, 3D numerical calculations of an S-Web arc driven continuously by realistic photospheric motions at its base. We present an analysis of the resulting magnetic field dynamics and subsequent plasma release, both near and far from the heliospheric current sheet. We consider our simulation results within the context of possible Parker Solar Probe and Solar Orbiter observations and make predictions for the structure and variability of the slow solar wind.

  • The multi-flux-rope system in solar active region

    Submitted by: Yijun Hou
    Authors: Yijun Hou, Jun Zhang, Ting Li, and Shuhong Yang (1. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China 2. School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China)
    Magnetic flux rope is a set of magnetic field lines winding around a central axis and is closely connected with solar eruptions, such as flares and coronal mass ejections. The classical scenario assumes a single flux rope for each eruption, but it is reasonable to expect multiple flux ropes in a complex active region (AR). Statistically investigating AR 11897, we verify the existence of multiple flux ropes during the evolution of this AR. Recently, AR 12673 in 2017 September produced the two largest flares in Solar Cycle 24: the X9.3 flare on September 6 and the X8.2 flare on September 10. The evolutions of the AR magnetic fields and the two large flares reveal that significant flux emergence and successive interactions between the different emerging dipoles resulted in the formations of multiple flux ropes and twisted loop bundles, which successively erupted like a chain reaction within several minutes before the peaks of the two flares. We propose that the eruptions of a multi-flux-rope system rapidly released enormous magnetic energy and resulted in the two largest flares in Solar Cycle 24.

  • Orbit and spot modelling of UX Arietis for the interpretation of radio flares

    Submitted by: Christian Hummel
    Authors: Christian Hummel (ESO)
    We observed the RS CVn-type binary UX Ari with the CHARA infared long-baseline interferometer and resolved the primary K2IV component in its orbit around the G4V secondary component. Combined with radial velocity measurements, the distance, masses, and luminosities of the stellar components could be obtained. Interferometric imaging with CHARA located a co-rotating spot on the primary during the month-long observation period. Using the orbit and light-curve modelling, we reconstruct the positions of the primary spot and the secondary component at several epochs at which radio observations with the VLBA detected flares. We try to relate the astrometry of the quiescent radio emission and the radio flares with the astrometry of the binary to distinguish between models of the radio emission based on magnetic loops anchored to the primary or flux tubes between the stellar components.

  • Landau fluid modeling of astrophysical plasmas - matching the fluid and collisionless kinetic descriptions

    Submitted by: Peter Hunana
    Authors: P. Hunana, A. Tenerani, G. P. Zank, E. Khomenko, M. L. Goldstein, G. M. Webb, M. Velli, L. Adhikari, M. Collados (Instituto de Astrofísica de Canarias)
    We will present a brief overview of collisionless fluid models that incorporate kinetic effects (such as Landau damping, finite Larmor radius corrections) into the fluid framework, and that are much closer to the collisionless kinetic description than traditional magnetohydrodynamics. It is the Landau damping that sharply separates traditional fluid models and collisionless kinetic theory, and the main reason why the usual fluid models do not converge to the kinetic description, even in the long-wavelength low-frequency limit. We start with a brief introduction to kinetic theory and we discuss the plasma dispersion function $Z(\zeta)$, and the associated plasma response function $R(\zeta) = 1 + \zeta Z(\zeta)$. We introduce the concept of Pad\´e approximants, that allows for the analytic approximation of the $Z(\zeta)$ and $R(\zeta)$ functions, by matching their power series and asymptotic series expansions. For some Pad\´e approximants of $R(\zeta)$, the possibility arises that the last retained moment, such as the heat flux or the 4th-order moment, can be expressed analytically through lower order moments. This constitutes a Landau fluid closure. Such closures are rare and the original closures constructed by Hammett and Perkins 1990 are often employed. We first consider a 1D (electrostatic) geometry and make a significant effort to map all possible Landau fluid closures that can be constructed at the 4th-order moment level. These closures for parallel moments have general validity from the largest astrophysical scales down to the Debye length, and we verify their validity by considering examples of the (proton and electron) Landau damping of the ion-acoustic mode, and the electron Landau damping of the Langmuir mode. We then consider a 3D (electromagnetic) geometry in the gyrotropic (long-wavelength low-frequency) limit and perform the same mapping. We proceed by considering 1D closures at higher-order moments than the 4th-order, and we show that it is possible to reproduce linear Landau damping in the fluid framework to any desired precision, thus showing the convergence of the fluid and collisionless kinetic descriptions.

  • How neural network helps to find sunspots and coronal holes

    Submitted by: Egor Illarionov
    Authors: E. Illarionov, A. Tlatov (Moscow State University, Kislovodsk Mountain Astronomical Station)
    A variety of practical neural networks examples opens a new approach to classical problems in solar data processing, in particular, to segmentation of sunspots and coronal holes in solar disk images. The point is that solar features catalogues produced by automatic routines are often weak consistent between each other and with visual expectation. This can be a manifestation of the fact that the objects under investigation are too complex to be described in an explicit form. In contrast, neural network is known as a universal approximator and we can hope to train a model to produce results similar to manual data processing. To support this idea we consider a database of the Kislovodsk Mountain Astronomical Station and modern neural network architectures. In our work we were able to train end-to-end models that demonstrate very natural sunspots and coronal holes segmentation in solar disk images. We discuss the obtained results and further applications of this approach.

  • TBC

    Submitted by: Lewis Ireland
    Authors:
    TBC nearer the time

  • 13,000 stars with spots in the Milky Way: spotted dwarfs and giants as a cosmic lab for studying stellar magnetism

    Submitted by: Patryk Iwanek
    Authors: Patryk Iwanek (Warsaw University Observatory)
    It is widely known that stellar spots are an indicator of stars' magnetic fields, thereby spotted stars are the best laboratory for testing the dynamo theory and improving theoretical models. I would like to present the discovery and statistical analysis of almost 13,000 stars with spots in the Milky Way, towards the Galactic bulge. Our study is based on a long-term, V- and I-band massive photometry obtained by the Optical Gravitational Lensing Experiment (OGLE) since the beginning of our project. We unveil two distinct groups of stars with spots based on their observational parameters, i.e. rotation periods and amplitudes of brightness. The first group contains dwarfs with rotation periods shorter than 2 days, and amplitudes smaller than 0.2 mag, while the second group consists of slowly-rotating (rotation periods up to 100 days) stars with amplitudes up to 0.7 mag. The latter group contains mostly spotted giants for which we discover dependence between luminosities and rotation periods. Our continuous observations have allowed us to discover two different correlations between changes in brightness and changes in color of spotted stars with their rotation. We are able to divide these stars into three groups according to the type of spots which prevails on their surfaces. During my talk, I will discuss possible explanations of such a division. We believe that these different manifestations of magnetic field are associated with different ways of generating it. Moreover, among all spotted stars we have found several dozen flaring objects. We discover that stars with larger spots coverage exhibit higher brightenings during outbursts. Additionally, I will present plans for future research of spotted stars within the OGLE survey.

  • Slingshot promiences in solar-like stars

    Submitted by: Moira Jardine
    Authors: Moira Jardine and Andrew Collier Cameron (University of St Andrews)
    "Slingshot" prominences have been observed for many years now on rapidly-rotating solar-like stars. The trapping of these cool condensations within the coronal magnetic field reveals the structure and dynamics of the stellar corona, and their centrifugal ejection augments the mass and angular momentum losses in the stellar wind. Recently, we have shown that observations of prominence masses and lifetimes allow us to measure the mass loss rate in the stellar wind. This is an important quantity as it governs the rotational evolution of the star, but is extremely difficult to measure by other means. Observations of slingshot prominences therefore provide a vital window into this aspect of stellar evolution and the impact of the star on the surrounding environment.

  • Long-term variations in the differential rotation correspond to the maxima and minima of the solar cycles 12-24

    Submitted by: Javaraiah Javaraiah
    Authors: J. Javaraiah (Formerly Indian Institute of Astrophysics, Bengaluru, India)
    Studies of variations in the solar differential rotation are important for understanding the underlying mechanism of solar cycle and other variations of solar activity. We analyzed the combined daily data of sunspot groups were reported by Greenwich Photoheliogrphic Results (GPR) during the period 1874-1976 and Debrecen Photoheliographic Data (DPD) during the period 1977-2017. We determined the equatorial rotation rate (A) and the latitude gradient (B) components of the solar differential rotation correspond to the maxima and minima of the solar cycles 12-14. We find that there exits a considerably significant secular decreasing trend in A correspond to the maxima of solar cycles. There exists no/negligible secular trends in A correspond to the minima of solar cycles and in B correspond to both the maxima and minima of solar cycles. We fitted a cosine-function to the values of A, and also to those of B, after removing the corresponding linear trends. The cosine-fits suggest that there exist 53.3-year and 83.2-year periodicities in A correspond to the maxima and minima of solar cycles, respectively, and 96.6-year and 75.5-year periodicities in B correspond to the maxima and minima of solar cycles, respectively. The maximum and minimum epochs of a solar cycle comprise relatively large and small numbers of large sunspot groups, respectively. The magnetic structures of large and small sunspot groups anchor at relatively deep and sallow layers of the solar convection zone, respectively. Hence, the periodicities in A and B correspond to the maxima and minima of solar cycles are different and might be originated at relatively deep and sallow layers of the solar convection zone, respectively.

  • The acticity cycles of Solar-type stars

    Submitted by: Sandra Jeffers
    Authors: S.V. Jeffers and the BCool collaboration
    The BCool project is an international collaboration studying the magnetic activity of low-mass stars from pre-main sequence through to evolved objects and using spectropolarimetric observations to directly characterise the large-scale magnetic fields of cool stars using Zeeman Doppler imaging. From our long-term monitoring of the large-scale magnetic field over more than 10 years, we are starting to see cyclic behaviour in several targets. In this presentation I will show our results and highlight a few cases we find surprising cyclic behaviour compared to the Sun.

  • The Impact of Stellar Activity on the Search for Terrestrial Exoplanets

    Submitted by: James Jenkins
    Authors: James Jenkins (Universidad de Chile)
    In this invited talk I will review the impact that stellar activity has on precision radial-velocity observations in the quest to discover the smallest exoplanets. I will discuss our methods to overcome these so-called 'jitter' effects, whilst highlighting some recent results on bright stars that have led to various controversies in the field. Finally, I will also briefly mention how the presence of activity can hinder precision transit photometry, particularly those observations that aim to search for the signatures of atmospheric chemistry in exoplanetary atmospheres.

  • Are there local dynamo actions in solar polar region?

    Submitted by: Chunlan Jin
    Authors: Chunlan Jin, Jingxiu Wang, Guiping Zhou, Yuzong Zhang (National Astronomy Observatories, Chinese Academy of Sciences)
    Polar magnetic field, as a component produced by the global dynamo, is thought to be the remnant of toroidal magnetic field transported poleward from Sun's active belts. In this study, we aim at exploring whether there is an operation of local dynamo in the solar polar region or not. Based on the long-term observations from the Helioseismic and Magnetic Imager (HMI) aboard Solar Dynamic Observatory, we find that the magnetic flux of the non-dominant polarity in the polar region (i.e., the region with the latitude higher than 60 degree) keep constant with the value of about 1$\times$10$^{21}$ Mx, which is 1/3 of total flux for the polar region in solar minimum of cycle 24. Furthermore, we track the bipole magnetic emergences (BMEs) in polar region identified from the observations of HMI and the Atmospheric Imaging Assembly. In totally, we have definitively identified 27 BMEs and 22 BMEs from the northern and southern polar regions, respectively. It is found that these BMEs tilt does not obey Joy's law of active region tilt, but shows a random state. These results indicate the existence of local dynamo actions in solar polar region.

  • Coronal Dimming as a Proxy for Stellar CMEs

    Submitted by: Meng Jin
    Authors: Meng Jin[1,2], Mark Cheung[2,3], Marc DeRosa[2], Kevin France[4], Adam Kowalski[4], James Mason[5], Rachel Osten[6] (1. SETI Institute; 2. Lockheed Martin Solar & Astrophysics Lab; 3. Hansen Experimental Physics Laboratory, Stanford University; 4. University of Colorado, Boulder; 5. NASA Goddard Space Flight Center; 6. Space Telescope Science Institute)
    Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with CMEs. Recent study found that coronal dimming is the only signature that could differentiate powerful flares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs by combining simulation and observational efforts. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we first demonstrate the model's capability to reproduce solar observations from SDO/AIA and EVE. We then extend the model for simulating CMEs on M dwarf stars by modifying the input magnetic field according to available stellar observations as well as the results from a stellar flux transport model. Using metrics such as dimming depth and dimming slope, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) and how these relationships could be used as a proxy for stellar CMEs.

  • Deciphering the solar cycle from tree rings

    Submitted by: Christoffer Karoff
    Authors: Christoffer Karoff et al (Aarhus University)
    Recent advances in accelerator mass spectroscopy measurements of radio carbon in tree rings now allow us to measure changes in radio carbon production rates in the Earth’s atmosphere caused by changes in the solar magnetic field with sub-annual resolution. These has proven to be very valuable for dating solar cosmic ray events – like the AD775 event. They also provide hope that we in the future will be able to the trace the solar cycle directly in the radio carbon measurements. In order to do this, we however, need numerous annual measurements as the uncertainty of the individual measurements is similar to the predicted amplitude of the solar cycle induced signal in the radio carbon production rates. If we succeed we would be able to trace the solar cycle back through the Holocene, which would provide us with valuable information for dynamo theory.

  • Tuning in to the radio environment of HD189733b

    Submitted by: Robert Kavanagh
    Authors: R. D. Kavanagh, A. A. Vidotto, D. Ó Fionnagáin (School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland)
    The winds of low mass stars, and their interactions with the magnetospheres of orbiting planets, are both expected to be sources of radio emission. If detectable, we would be able to constrain the properties of stellar winds and exoplanetary magnetospheres, and directly detect exoplanets. Here, we predict the radio emission of the hot Jupiter HD189733b and the wind of its host star. We model the stellar wind using magnetic field maps observed at three different epochs. With that, we model the planetary radio emission using the radiometric Bode’s law. For planetary magnetic field strengths between 1 to 10 G, we estimate that the planet emits at frequencies of 2 to 25 MHz, irrespective of the epoch or orbital phase of the planet, with peak flux densities of ~ 100 mJy. We numerically solve the equations of radiative transfer for the stellar wind, and find that it becomes optically thin above 10 GHz. As the planet emits at frequencies below this value, regions of the stellar wind are optically thick to the emitted planetary frequency. Therefore, the planetary radio emission can only propagate out of the system and reach the observer for a fraction of the orbital period.

  • Generation and dissipation of Alfven waves in partially ionized solar atmosphere

    Submitted by: Elena Khomenko
    Authors: E. Khomenko(1), P. Cally(2), P. Gonzalez-Morales(1), N. Vitas(1), M. Collados(1) ((1) Instituto de Astrofisica de Canarias, Spain; (2) School of Mathematical Sciences, Monash University, Australia)
    In this contribution we study the influence of partial ionization of solar plasma into the generation, dissipation and heating due to Alfven waves. We will summarize the results of our simplified models on how the Alfven waves can be generated due to the Hall effect or via the mode transformation enhanced in the presence of small-scale flux tubes. The conclusions from idealized simulations have been checked using realistic 3D radiative-MHD simulations of solar magneto-convection that include battery, ambipolar and Hall effects all together. Ambipolar diffusion causes important effects on the amplitudes of waves excited by convection in the simulations, and produces a significant absorption of Poynting flux, that results in chromospheric heating. The Hall effect acts into the direction of significantly increasing the Poynting flux due to Alfven waves to the upper chromospheric layers.

  • 3D Realistic Modeling of Solar Turbulent Dynamics from Subsurface to the Chromosphere and Corona

    Submitted by: Irina Kitiashvili
    Authors: I. N. Kitiashvili(1), A. A. Wray(1), A. G. Kosovichev(2), V. M. Sadykov(2), N. N. Mansour(1) (1) NASA Ames Research Center, 2) NJIT)
    Realistic radiative modeling of solar dynamics is an important tool for understanding small-scale processes on the Sun, which usually are not well resolved in observations. To study the complex and multi-scale nature of the turbulent subsurface and atmospheric dynamics of the Sun we have developed the StellarBox code (Wray et al., 2018). It allows us to perform realistic-type modeling based on first physical principles, in which unresolved turbulent dynamics is approximated using sub-grid turbulence models. Using 3D realistic radiative MHD simulations we can reproduce the dynamics observed in the surface layers and investigate interactions with the chromosphere. In this presentation, we will present simulations of a small-scale dynamo process and eruptive activity in the presence of magnetic fields. In addition, we will discuss the effects of magnetic fields on the excitation of acoustic waves beneath the solar surface as well as on the dynamics and structure of the chromosphere and corona. The modeled properties will be compared with observations from the SDO, Hinode, and IRIS missions.

  • Concepts of the Solar and Stellar Dynamos and Convection

    Submitted by: Irina Kitiashvili
    Authors: Irina N. Kitiashvili (NASA Ames Research Center)
    The complex multiscale dynamics of turbulent flows and magnetic fields generated by the turbulent dynamo inside the Sun are the source of various manifestations of solar activity, which in turn create an unsteady space environment and affect space-weather conditions. In general, solar dynamo processes fall into two basic categories: a large-scale global dynamo that is responsible for activity cycles and a small-scale turbulent or local dynamo that creates the Sun’s “magnetic carpet”. The interior dynamics of other stars may significantly deviate from solar conditions, because of different initial conditions (mass, chemical composition, etc.) and evolutionary paths, and may lead to convective flows and dynamo processes for which the separation into global and local dynamos is less clear. Recent advances in computational capabilities and in observational data allow us to make progress in understanding stellar dynamics and magnetic activity. In the talk I will give a brief overview of numerical studies of the convective structure and dynamo operation across various stellar types.

  • Global Evolution of Solar Magnetic Fields and Prediction of Solar Activity Cycles

    Submitted by: Irina Kitiashvili
    Authors: Irina Kitiashvili (NASA Ames Research Center)
    Prediction of solar activity cycles is challenging because the physical processes inside the Sun involve a broad range of multiscale dynamics that no model can reproduce, and the available observations are highly limited and cover mostly surface layers. Helioseismology makes it possible to probe solar dynamics in the convective zone, but variations in the differential rotation and meridional circulation are currently available for only two solar activity cycles. It has been demonstrated that sunspot observations, which cover over 400 years, can be used to calibrate the Parker-Kleeorin-Ruzmaikin model and that the Ensemble Kalman Filter (EnKF) method can be used to link the model magnetic fields to sunspot observations to make reliable predictions of a following cycle. However, for more accurate predictions, it is necessary to use actual observations of the solar magnetic fields, which are available for only four solar cycles. This raises the question of how limitations in observational data and model uncertainties affect predictive capabilities and implies the need for the development of new forecast methodologies and validation criteria. In this presentation, I will discuss the influence of the limited number of available observations on the accuracy of EnKF estimates of solar cycle parameters.

  • Structure and Dynamics of the Overshoot Layer in a Rotating Main-Sequence Star a with Shallow Convection Zone

    Submitted by: Irina Kitiashvili
    Authors: Irina N. Kitiashvili, Alan A. Wray (NASA Ames Research Center)
    Current state-of-the-art of computational modeling makes it possible to build realistic models of stellar convection zones and atmospheres, which can take into account chemical composition, radiative effects, ionization, and turbulence. The standard 1D mixing-length-based evolutionary models are not able to capture the many physical processes of stellar interior dynamics, but they provide an initial approximation of stellar structure that can be used to initialize 3D time-dependent radiative hydrodynamics simulations, based on first physical principles, that take into account the effects of turbulence, radiation, and other phenomena. In this presentation we will show simulation results from a 3D realistic modeling of an F-type main-sequence star of 1.47 solar mass, in which the computational domain includes the upper layers of the radiation zone, the entire convection zone, and the photosphere. This simulation provides new insight into the formation and properties of the convective overshoot region, the dynamics of the near-surface, highly turbulent layer, and the structure and dynamics of granulation. We will discuss the thermodynamic structure and the effects of rotation on the dynamics of the star across these layers.

  • Magnetic field changes in flares

    Submitted by: Lucia Kleint
    Authors: L. Kleint (1,2), M. Wheatland (3), A. Mastrano (3), P. McCauley (3) (1) Leibniz-Institut für Sonnenphysik, Germany, 2) University of Applied Sciences and Arts Northwestern Switzerland, Switzerland, 3) Sydney Institute for Astronomy, University of Sydney, Australia)
    Flares are highly energetic eruptions on the Sun and stars and occur because of the reconnection of magnetic field lines. Their energy is dissipated as particle acceleration, heating, radiation, but also by inducing changes of magnetic fields in the lower solar atmosphere. Stepwise and rapid changes of photospheric magnetic fields are observed in most flares, but cannot be explained by models yet. To investigate the origin of the field changes and to probe energy dissipation mechanisms, we analyze the so far only simultaneous photospheric and chromospheric observation of flare-related magnetic field changes. The unique polarimetric observations of the X1 flare on 2014-03-29 show that chromospheric changes are stronger, occur in larger areas, and are located near the footpoints of loops, in contrast to photospheric changes, which predominantly appear near polarity inversion lines. They however do not coincide with other flare-related phenomena, such as X-rays, continuum emission, or a small sunquake, making their origin puzzling. We carry out non-linear force-free field modeling based on SDO/HMI 135s fast-cadence vector magnetograms and compare the field changes in the observations to the model, at photospheric and chromospheric heights. The chromospheric changes appear very different in the model, and we conclude that a force-free model may not be sufficiently realistic and that the observed changes likely require changes in the magnitude of the field, not just in its direction.

  • The magnetic structure and dynamics of a decaying active region

    Submitted by: Ioannis Kontogiannis
    Authors: Ioannis Kontogiannis (1), Christoph Kuckein (1), Sergio Javier González Manrique (2), Tobias Felipe (3,4), Meetu Verma (1), Horst Balthasar (1) and Carsten Denker (1) (1 Leibniz-Institut für Astrophysik Potsdam (AIP), Germany ; 2 Astronomical Institute, Tatranská, Lomnica, Slovak Republic; 3 Instituto de Astrofísica de Canarias, La Laguna, Spain; 4 Universidad de La Laguna, Tenerife, Spain)
    We study the evolution of the decaying active region NOAA AR 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations, taken on May 9, 2018. We utilize spectropolarimetric scans at the 10830 Å spectral range GREGOR Infrared Spectrograph (GRIS), spectral imaging time series in the NaI D2 spectral line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context imaging in the CaII H and blue continuum by the High-resolution Fast Imager (HIFI). Context imaging in the UV/EUV from SDO and IRIS raster scans complement our data set. The region under study contains one pore with a light bridge, a few micro-pores and extended clusters of magnetic bright points. The magnetic structure from the photosphere up to the chromosphere and the corona is reconstructed using spectropolarimetric inversions of the Stokes profiles of the CaI, SiI and HeI lines and magnetic field extrapolations. The dynamics of the lower chromosphere and upper photosphere is revealed by modelling the NaI D2 spectral imaging information and the photospheric flow field is deduced by means of Local Correlation Tracking. The high resolution photospheric imaging reveals, in unprecedented detail, the complex interaction between granular-scale convective motions and a range of scales of magnetic field concentrations. The pore itself shows a strong interaction with the convective motions which eventually leads to its decay, while, under the influence of the photospheric flow field, micro-pores appear and disappear. During this process, compressible waves are generated which are guided towards the upper atmosphere along the magnetic field lines of the various magnetic structures within the field of view. Modelling of the HeI absorption profiles reveals high velocity components, mostly associated with magnetic bright points at the periphery of the active region, many of which correspond to asymmetric SiI Stokes V profiles revealing a coupling between upper photospheric and upper chromospheric dynamics. Time-series of NaI D2 spectral images reveal episodic high velocity components at the same locations. State-of-the-art multiwavelength GREGOR observations allow us to track and understand the mechanisms in act during the decay phase of the active region.

  • Parker Solar Probe SWEAP thermal plasma measurements from the first encounter

    Submitted by: Kelly Korreck
    Authors: K. Korreck(1), J. Kasper(2), A. Case (1),D. Larson (3), R. Livi(3), M. Stevens (1), P. Whittlesey (3) for The SWEAP Team (1- Smithsonian Astrophysical Observatory; (2)University of Michigan Ann Arbor; (3) University of California Berkeley)
    NASA's Parker Solar Probe with the SWEAP thermal plasma instrument suite aboard made its first encounter with the Sun in November 2018. Being closer to the Sun than any previous spacecraft, Parker Solar Probe employs a combination of in situ measurements and imaging to achieve the mission's primary scientific goal: to understand how the Sun's corona is heated and how the solar wind is accelerated. The Solar Wind Electron Alphas and Protons (SWEAP) instrument suite consists of a Faraday cup and three electrostatic analyzers (ESAs). Together these sensors detect the solar wind plasma that the Parker Solar Probe Spacecraft will encounter. In order to accomplish the science objectives of Parker Solar Probe, an encounter based operations scheme is utilized. A summary of the SWEAP data from the first orbit will be presented. Future plans for data collection will also be discussed.

  • Dynamo Wave Patterns Inside the Sun Revealed by Tor- sional Oscillations

    Submitted by: Alexander Kosovichev
    Authors: Alexander G. Kosovichev (NJIT, U.S.A.) & Valery V. Pipin (Institute for Solar-Terrestrial Physics, Russia)
    Torsional oscillations represent bands of fast and slow zonal flows around the Sun, which migrate during solar cycles towards the equator following the sunspot butterfly diagram. Principal component analysis of helioseismology data obtained in 1996-2018 for almost two solar cycles reveals zones of deceleration of the torsional oscillations inside the Sun due to back reaction of dynamo-generated magnetic field. The flow deceleration originates in the solar tachocline at high latitudes, and migrates through the convection zone revealing patterns of magnetic dynamo waves. The analysis explains the phenomenon of the ‘extended solar cycle’ observed in the evolving shape of the solar corona, and why the polar magnetic field strength predicts the solar maxima. The results indicate further decline of sunspot activity in the next solar cycle.

  • Geomagnetically induced currents related to impulsive events at low latitudes

    Submitted by: N'Guessan Kouassi
    Authors: N'Guessan KOUASSI, VAFI DOUMBIA (Université Félix Houphouet Boigny Abidjan - Cote d' ivoire)
    Intense space weather events (geomagnetic storms and sub-storms) are potential sources of electric induction within the Earth. Disruptions of technological equipments due to “Geomagnetically Induced Currents (GICs)” are experienced in the Scandinavian countries since mid XIXth century (Pulkkinen, 2003). Due to the harmful impacts of GICs on technological devices, the GICs have been mostly investigated at high latitudes (Pulkkinen et al., 2001a, 2001b, 2003, 2007). There are reports on GIC causing perturbation in technological structures in mid- and low-latitude (Ngwira et al., 2008; Torta et al., 2012, Trivedi et al., 2007). Due to these threats, we study the GICs at low latitudes namely in West Africa. In our study, we estimate the geoelectric field from the magnetic data and compare it to the measured geoelectric field. We note that our results are in good agreement with the measures. Then, we estimate the intensity of the GICs from the geoelectric field calculated on the one hand and on the other hand, from the measured geoelectric field.

  • Magnetized downflows in the chromosphere

    Submitted by: Sowmya Krishnamurthy
    Authors: Sowmya Krishnamurthy, Andreas Lagg, Sami K. Solanki (Max Planck Institute for Solar System Research)
    Supersonic downflows in the chromosphere associated with magnetic fields have been reported based on the diagnostics with He I 10830 lines. However, a comprehensive study of their characteristics is still missing. We investigate the velocity pattern and magnetic fields in the upper chromosphere using the spectropolarimetric data of active regions from the GREGOR telescope recorded between 2014 and 2017. We find supersonic downflows to be present in all the active regions studied, with some showing dual distribution in the downflow velocities. Emerging active regions harbour most of the observed downflows. Filaments, arch filament systems, periphery of pores, loops above light bridges, penumbra and umbral regions in our data sample host supersonic downflows. The draining of the material from the loops towards the photosphere turns out to be a plausible mechanism behind these chromospheric downflows associated with emerging magnetic flux and arch filament systems.

  • Diagnosing chromospheric magnetic field through simultaneous spectropolarimetry in Hα and Ca II 854.2 nm

    Submitted by: Nagaraju Krishnappa
    Authors: K. Nagaraju (Indian Institute of Astrophysics)
    Chromosphere is a dynamic layer of solar atmosphere providing a crucial interface between photosphere and corona. Measurement of magnetic field in this layer is challenging both from point of view of observations and interpretation of the data . The spectral line due to singly ionized Ca at 854.2 nm (CaNIR) is one of the most widely used spectral lines for chromospheric magnetic field diagnostics. Though challenges exist, most often interpretation of the spectropolarimetric data of CaNIR is carried out through inversions. We present in this work about simultaneous spectropolarimetric observations of sunspots/pore in CaNIR and Hα both from SPINOR instrument at Dunn Solar Telescope and a recently installed polarimeter at Kodaikanal Tower Tunnel Telescope. Since interpretation of CaNIR data through inversion is better understood than those of Hα data, model atmosphere will be calculated using CaNIR data and then using this model Hα line profiles will be synthesized and compared with the observed profiles. By doing this we hope to understand better the Hα line formation in the magnetic field regions. Inversion of Hα spectropolarimetric data will also be attempted with the model atmosphere calculated using CaNIR line as an initial guess model.

  • Coordinated observations between China and Europe to follow the active region NOAA 12709

    Submitted by: Christoph Kuckein
    Authors: Sergio J. González Manrique1, Christoph Kuckein2, Peter Gömöry1, Shu Yuan3, Zhi Xu4, Ján Rybák1, Horst Balthasar2, Pavol Schwartz1, and Július Koza1 (1. Astronomical Institute, Slovak Academy of Sciences, Slovakia 2. Leibniz Institut für Astrophysik Potsdam, Germany 3. Laboratory of Astronomical technology, YNAO, China 4. Fuxian Solar Observatoy, YNAO, China)
    As part of a joint effort between three observatories (China-Europe) we present the first images of a coordinated campaign following active region NOAA 12709 on 2018 May 13. The active region was close to disk center and enclosed two small pores seen in the photosphere and filamentary structures in the chromosphere. We observed the active region at the 1.5-meter GREGOR solar telescope on Tenerife (Spain) with spectropolarimetry using the GREGOR Infrared Spectrograph (GRIS) in the He I 10830 Å spectral range. GREGOR also provided context images with the High-Resolution Fast Imager (HiFI) with two filter channels at Ca II H 3968 Å and blue continuum at 4505 Å. The Lomnicky Peak Observatory (Slovakia) recorded the active region with the new Solar Chromospheric Detector (SCD) in spectroscopic mode at Hα 6562 Å. The Fuxian Solar Observatory (China) observed the active region with the 1-meter New Vacuum Solar Telescope (NVST), using the Multi-Channel High Resolution Imaging System at Hα 6562 Å. Overlapping images of the active region from all three telescopes will be shown as well as preliminar Doppler line-of-sight velocities. The potential of such observations are discussed.

  • Magnetic properties of small solar intergranular bright points inferred from near infrared lines

    Submitted by: Christoph Kuckein
    Authors: Christoph Kuckein (Leibniz Institute for Astrophysics Potsdam)
    Photospheric bright points are the smallest observable manifestations of the magnetic field on the solar surface. However, they remain challenging to observe due to atmospheric seeing and limiting spatial resolution of current telescopes. In this work, we present a data set acquired with Europe's largest solar telescope, the 1.5-meter GREGOR telescope, with multiple instruments, from the visible blue to the near infrared spectral range. Filtergrams of 450 nm (blue continuum) and Ca II H at 396 nm were used to identify photospheric small-scale intergranular bright points. Simultaneous observations with the spectrograph in the He I 1083 nm spectral range allowed for spectropolarimetric measurements in the photosphere and chromosphere. To the best of our knowledge, this spectral range has not been explored so far to analyze photospheric (magnetic) bright points. The spectropolarimetric data was exploited using the Stokes Inversions based on Response functions (SIR) code. The obtained magnetic field stratification with height, together with an analysis of the LOS velocities, in and around bright points will be discussed in the context of small-scale flux-tube models and simulations.

  • Revisiting the building blocks of solar magnetic fields by GREGOR

    Submitted by: Christoph Kuckein
    Authors: D. Utz 1,2; C. Kuckein 3; J. I. Campos Rozo, 1,4; S. J. Gonzalez Manrique 5; H. Balthasar, 3; P. Gömöry, 5; J. Koza, 5; J. Palacios, 6; C. Denker 3; M. Verma 3; I. Kontogiannis 3; K. Krikova 1; S. Hofmeister 1; A. Diercke 3 (1) IGAM, Univ. Graz, Austria; 2) IAA-CSIC, Granada, Spain; 3) AIP, Potsdam, Germany; 4) OANC, Univ. Nacional de Colombia, Bogota, Colombia; 5) AISAS, Tatranska Lomnica, Slovakia; 6) KIS, Freiburg, Germany.)
    The Sun is our dynamic host star due to its magnetic fields which cause plentiful of activity in its atmosphere. Starting from high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about the formation and evolution of solar magnetic fields. These fields exist on a large variation of spatial and temporal scales starting on the larger end with active regions harbouring complex sunspots, via isolated pores, down to the smallest yet resolved elements - so-called magnetic bright points (MBPs). In this poster contribution we want to revisit the various mentioned manifestations of solar magnetic fields by the largest European solar telescope in operation, the 1.5-meter GREGOR telescope. We will show high-resolution images from the High-Resolution Fast Imager (HiFI) and spectro-polarimetric data from the GREGOR Infrared Spectrograph (GRIS). Besides, we will outline resolved convective features inside the larger structures - so-called lightbridges. Clearly such magneto-convective features happen on large to mid-sized scales (from sunspots to pores) giving rise to the question if such features can also occur within the smallest yet detected features - the MBPs?

  • Cycle Period, differential rotation, and meridional flow of early M dwarf stars

    Submitted by: Manfred Küker
    Authors: M. Küker, G. Rüdiger, K. Olah, K. Strassmeier (Leibniz-Institut für Astrophysik Potsdam; Konkoly Observatory Budapest)
    Recent observations suggest the existence of two characteristic cycle times for early-type M stars dependent on the rotation period. They are of order one year for fast rotators (Prot < 1 day) and of order four years for slower rotators. Additionally, the equator-to-pole differences of the rotation rates with δΩ up to 0.03 rad d−1 are known from Kepler data for the fast-rotating stars. These values are well-reproduced by the theory of large-scale flows in rotating convection zones on the basis of the Λ effect. The resulting amplitudes um of the bottom value of the meridional circulation allows for the calculation of the travel time from pole to equator at the base of the convection zone of early-type M stars. These travel times strongly increase with rotation period and they always exceed the observed cycle periods. Therefore, the operation of an advection-dominated dynamo in early M dwarfs, where the travel time must always be shorter than the cycle period, is not confirmed by our model nor the data.

  • Numerical simulations of Alfvén and magnetoacoustic waves in a finely-structured solar magnetic flux tube

    Submitted by: Błażej Kuźma
    Authors: Błażej Kuźma, Kris Murawski (Maria Curie-Sklodowska University, Lublin, Poland)
    We numerically solve 3D magnetohydrodynamic equations for a stranded magnetic flux tube in the solar atmosphere. This flux tube is perturbed by a periodic driver in the azimuthal component of plasma velocity. As result, we observe torsional Alfvén and fast magnetoacoustic kink waves being guided upward along the strands. We conclude that a substantial part of waves energy flux is carried to upper layers of the solar atmosphere, contributing to its heating.

  • MCMC inversion of the Stokes profiles

    Submitted by: Hao Li
    Authors: Hao Li (Yunnan Observatories, Chinese Academy of Sciences)
    Stokes inversion techniques, based on the analyzation of polarization in spectral lines, are the most powerful tools to obtain the information about the magnetic and thermodynamic quantities in the solar atmosphere. In this paper, we present a Milne-Eddington inversion code based on Bayesian inference, which is often implemented with the Markov chain Monte Carlo (MCMC) simulation. This kind of simulation is a random sampling method to visit a point in the parameter space with a probability proportional to the distribution function, and furthermore provides a powerful way to infer the parameters of a model, their errors, and mutual correlations between each parameter. Detailed tests of the code with synthetic profiles and Hinode/SP observations manifest the applicability of this technique to infer the magnetic field and the errors. The spatial distribution of physical quantities and their errors are estimated according to the posterior probability distribution. We find that the errors of B, θ, φ, Bx, and By are smaller in the quiet regions than in the active regions. In contrast, the errors of Bz do not present much difference between quiet and active regions. Besides, the mutual correlations between each model parameter are also investigated. We find that most of the thermodynamic parameters are strong correlated, while the correlations between the thermodynamic and magnetic field parameters are weak.

  • Diagnosing perspective of CME with the Lyman-alpha Solar Telescope

    Submitted by: Hui Li
    Authors: Hui Li & LST Team (Purple Mountain Observatory)
    The Lyman-alpha Solar Telescope is to be launched in early 2022 with the Advanced Space-based Solar Observatory (ASO-S) mission. LST will provide high tempo-spatial resolution images of the full-disk of the Sun (up to 1.2 solar radii) and the inner solar corona from 1.1 – 2.5 solar radii in both the hydrogen Lyman-alpha line (121.6nm) and white-light wavebands, and monitor solar activities on the disk and in the corona and track their evolution from disk center up to 2.5 solar radii. Thanks to the combination of observation wavebands, LST has its own capabilities in studying solar eruptions, including solar flares, coronal mass ejections (CMEs), prominence eruptions, etc., and diagnosis of their physical parameters, such as density, velocity and temperature of CMEs. In the talk, I will introduce the LST payload briefly and speak about the diagnosing perspectives of LST for the study of solar eruptions with emphasis on CME investigation.

  • Solar Rossby waves from 21 years of SOHO/MDI and SDO/HMI observations

    Submitted by: Zhi-Chao Liang
    Authors: Z.-C. Liang [1], L. Gizon [1,2], A. C. Birch [1], T. L. Duvall, Jr. [1] ([1] Max Planck institute for Solar system research, [2] Georg-August-Universitaet Goettingen, Institut fuer Astrophysik)
    Solar equatorial Rossby waves have recently been detected on the Sun by Loeptien et al. (2018). Here we apply time-distance helioseismology to twenty-one years of data from SOHO/MDI and SDO/HMI with the aim of extending the previous findings to a longer period and deeper layers. North-south helioseismic travel-time shifts are measured along the solar equator that are sensitive to flows down to about 0.91 solar radius. The Rossby modes are detected in the power spectra of the data for azimuthal wavenumbers ranging from m=3 to m=15, with mode parameters that are consistent with or close to the ones reported by Loeptien et al. (2018). We estimate that the maximum surface velocity of each mode is on the order of 1 to 3 m/s. In addition, we will report on the time dependence of the amplitudes and frequencies of these modes.

  • Examining the optical intensity and magnetic expansion factor in the open magnetic regions associated with coronal holes

    Submitted by: Chia-Hsien Lin
    Authors: Chia-Hsien Lin(1), Guan-Han Huang(1), Lou-Chuang Lee(2) ((1) Graduate Institute of Space Science, National Central University, Taiwan; (2) Institute of Earth Sciences, Academia Sinica, Taiwan)
    Coronal holes are the darkest regions in soft X-ray or some coronal temperature images. The magnetic field lines inside the coronal holes are usually thought to extend far away from the Sun, that is, ``open''. Such open magnetic field configuration allows large amount of plasma flow into interplanetary space, resulting in lower plasma density and therefore lower optical emission in the source region. Because of the association between the low optical emission and open magnetic field structure, coronal holes and open magnetic field regions are often considered to be same regions, in the statistical sense. However, our study reveals that only 13% of open magnetic field regions are coincident with coronal holes. The aim of this study is to investigate the conditions that affect the optical emission intensity of an open magnetic field region. Our results indicate that the optical intensity and the magnetic field expansion factor of the open magnetic field regions are weakly positively correlated when plotted in logarithmic scale, and that the bright open magnetic field regions are likely to locate inside or next to the regions with closed field lines.

  • Probing solar-cycle variations of magnetic fields in the convection zone using meridional flows

    Submitted by: Chia-Hsien Lin
    Authors: Chia-Hsien Lin (1) and Dean-Yi Chou (2) ((1) National Central University, Taiwan; (2) National Tsing-Hua University, Taiwan)
    Solar meridional flows are axisymmetric flows on meridional planes. Here we study their solar-cycle variations in the convective zone using SOHO/MDI helioseismic data from 1996 to 2010, which includes two solar minima and one maximum. The travel time difference between northward and southward waves is measured with the time-distance method as a function of travel distance, latitude, and time. An inversion method is applied to invert the travel time difference to obtain meridional flows at the minimum and the maximum. At the minimum, the flow has a three-layer pattern: poleward in the layer above 0.86R, equator-ward between 0.74 and 0.86R, and poleward below 0.74R. The flow pattern changes significantly from the minimum to the maximum. The change above 0.9R indicates two phenomena: first, the flow speed is reduced at the maximum; second, a convergent flow centered at the active latitudes is generated at the maximum. These two phenomena are consistent with the surface meridional flows measured with surface tracers in the previous study. The flow change extends all the way down to 0.68R, and the pattern is more complicated. However, it is clear that the active latitudes play a role in the flow change. This suggests that magnetic fields are responsible for the flow change, which could be used to probe the solar cycle variations of magnetic fields in the deep convection zone.

  • Solar open magnetic flux migration pattern over solar cycles

    Submitted by: Chia-Hsien Lin
    Authors: Chia-Hsien Lin (1), Guan-Han Huang (1) and Lou-Chuang Lee (2) ((1) National Central University, Taiwan; (2) Academia Sinica, Taiwan)
    The objective of this study is to investigate the solar-cycle variation of the areas of solar open magnetic flux regions at different latitudes. The data used in this study are the radial-field synoptic maps from Wilcox Solar Observatory from May 1970 to December 2014, which covers 3.5 solar cycles. Our results reveal a pole-to-pole trans-equatorial migration pattern for both inward and outward open magnetic fluxes. The pattern consists of the open flux regions migrating across the equator, the regions generated at low latitude and migrating poleward, and the regions locally generated at polar regions. The results also indicate the destruction of open flux regions during the migration from pole to equator, and at low latitude regions.

  • Historical catalog of Sunspots and Its Physical Parameters in China

    Submitted by: Ganghua Lin
    Authors: Ganghua Lin, X.F. Wang ,·S. Liu ,· X. Yang, G.F. Zhu, Y.Y. Deng, · H.S. Ji, · T.H. Zhou, · L.N. Sun, J. Lin, · Y.L. Feng, · Z.Z. Liu, · J.P. Tao, · M.X. Ben, · M.D. Ding, · Z. Li , · S. Zheng, · S.G. Zeng , · H.L. He, · X.Y. Zeng, · Y. Shu, · X.B. Sun (National Astronomical Observatories, Chinese Academy of Sciences)
    Based on the Chinese historical sunspots drawings, a data set consisting of the scanned images and all their digitized parameters from 1925 to 2015 have been constructed. In this poster, we describe the developmental history of sunspots drawings in China. We also describe the processing procedure from inputting the raw image into the scanning equipment until these extracted parameters. In a country spanning 60 degrees from east to west and 50 degrees from north to south, our data set fills the historical gap of almost ninety years which is with consistency standards, time continuity, and digitization of sunspots observation. As a complementary to other sunspots observation in the world, we provided abundant information to the long term solar cycles solar activity research.

  • The coronal emission lines monitoring

    Submitted by: Yu Liu
    Authors: Yu Liu, Xuefei Zhang, Mingyu Zhao, Tengfei Song (Yunnan Observatories, CAS)
    The particular environment with high temperature and low plasma density in the corona results to the formation of some forbidden emission lines have been utilized to diagnose the corona for a few decades. For these forbidden lines formed in the corona, besides their contribution on revealing the long-term coronal cycles as well as their relationship to the other solar phenomena, it is also helpful to detect limb coronal waves and ejections originated from the lower corona which seems not to be paid close attention to. We present our recent work with data from our Lijiang coronagraph and the other instruments. Suggestions are presented that we not only need to keep the traditional coronal emission line observations as a routine task for current coronagraph observations, but need to develop larger coronagraphs with advanced technology.

  • The Sun as an exoplanet host star

    Submitted by: Joe Llama
    Authors: Joe Llama (Lowell Observatory)
    he Sun offers a unique opportunity to study the impact of stellar activity on both the detection and characterization of exoplanets. NASA's Solar Dynamics Observatory has been observing the Sun continuously since April 2010 with unprecedented coverage and wavelength coverage. High energy observations of transiting exoplanets have revealed the presence of extended atmospheres around a number of systems. At such high energies, stellar radiation is absorbed high up in the planetary atmosphere, making X-ray and UV observations a potential tool for investigating the upper atmospheres of exoplanets. However, at these high energies, stellar activity can dramatically impact the observations. At short wavelengths, the stellar disk appears limb-brightened, and active regions appear as extended bright features that evolve on a much shorter timescale than in the optical. These features impact both the transit depth and shape, affecting our ability to measure the true planet-to-star radius ratio. In this presentation, I will show the results of simulated exoplanet transit light curves using Solar data obtained in the soft X-ray and UV by the Atmospheric Imaging Assembly onboard NASA's Solar Dynamics Observatory to investigate the impact of stellar activity at these wavelengths. By using a limb-brightened transit model coupled with disk resolved Solar images in the X-ray, extreme- and far-UV I will show how both occulted and unocculted active regions can mimic an inflated planetary atmosphere by changing the depth and shape of the transit profile. I will also show how the disk-integrated Lyman-alpha Solar irradiance varies on both short and long timescales and how this variability can impact our ability to recover the true radius ratio of a transiting exoplanet. Finally, I will present techniques on how to overcome these effects to determine the true planet-to-star radius in X-ray and UV observations.

  • The past and the future of the Sun: What solar twins can tell us about the solar magnetic and rotational evolution?

    Submitted by: Diego Lorenzo de Oliveira
    Authors: Diego Lorenzo-Oliveira,$^{1}$; Jorge Meléndez,$^{1}$; Jhon Yana Galarza,$^{1}$; Geisa Ponte$^{2}$; Leonardo A. dos Santos$^{3}$; Lorenzo Spina$^{4}$; Megan Bedell$^{5}$; Iv\'an Ram\'{i}rez$^{6}$; Jacob L. Bean$^{7}$; Martin Asplund$^{8}$ ((1) Universidade de Sao Paulo; (2) Universidade Federal do Rio de Janeiro; (3) Observatoire astronomique de l’Université de Genève; (4) Monash Centre for Astrophysics; (5) Center for Computational Astrophysics; (8) The Australian National University)
    Rotation-based ages of old Sun-like stars are rooted in a complex and intricate dependence on age, rotation, turbulent convection, structural variations and mass-loss due to magnetized winds. Classically, the age-dating method that relies on this phenomenon assumes that the rotational periods can be expressed in well-defined functions of the age and mass, the so-called gyrochronology relations. These relations had successfully confirmed the paradigm of rotation-activity-age coupling that powers the global dynamo evolution along the main-sequence and reproduced the main features observed in open clusters spanning a wide range of ages. However, in the light of Kepler data, the presence of apparently old and fast rotators that do not obey the usual gyrochronology relations led to the hypothesis of weakened magnetic breaking in some stars. We approached this problem by using a selected sample of solar twins and building a grid of rotational tracks as function of age, mass and metallicity over a large range of possible critical Rossby number to account for the magnetic weakened braking phenomena observed in the Kepler sample. In the light of our solar twin sample, we found a marginal statistical evidence favoring the smooth rotation evolution (critical Rossby number solution ~2.6, or ages greater than ~8 Gyr). The lower limit of critical Rossby number found is greater than 2.3 or older than 5.3 Gyr (at 95% confidence level) for a solar mass/metallicity star. These limits intercept an age range somewhat older than the Sun and the end of the main-sequence. This study highlights the difficulty to statistically discern both scenarios with the current sample of solar twins.

  • Solar Activity Influences on Planetary Atmosphere Evolution: Lessons from Observations at Venus, Earth, and Mars

    Submitted by: Janet Luhmann
    Authors: Janet G. Luhmann (Space Sciences Laboratory, University of California, Berkeley, CA 94720)
    The Pioneer Venus and Venus Express missions, the Mars Express and MAVEN missions, together with numerous Earth orbiters carrying space physics and aeronomy instruments, have combined with the increasing availability of space weather observations to provide good ideas of the impacts of present-day solar activity on the atmospheres of terrestrial planets. Of most interest among these are the responses leading to escape of either ion or neutral constituents-potentially altering both the total atmospheric reservoirs and their composition. While debates continue regarding the role(s) of a planetary magnetic field in either decreasing or increasing these escape rates, numerous observations have shown that enhancements can occur in response to many combinations of solar activity-related changes. These generally involve increased energy inputs to the upper atmospheres, increases in ion production, and/or increases in escape channels, e.g. via interplanetary field penetration or planetary field 'opening'. The problems come when extrapolations of these loss rates back in time are needed. While it is probably safe to suggest lower limits based simply on planet age multiplied by currently measured ion and neutral escape rates, the evolution of the Sun, including its activity, must be folded into these estimations. Poor knowledge of the history of solar activity, especially in terms of coronal mass ejections and solar wind properties, greatly compounds the uncertainties in related planetary atmosphere evolution calculations. Prospects for constraining their influences will depend on our ability to do a better job of solar activity history reconstruction.

  • New Chromospherically Young and Kinematically Old objects (CYKOs) candidates

    Submitted by: Eduardo Machado-Pereira
    Authors: Eduardo Machado Pereira, Helio Jaques Rocha Pinto (Observatório do Valongo (UFRJ))
    Stellar ages can be determined through a variety of methods, one of those based on the chromospheric activity (CA) of the star, derived from Ca II H-K reversals. The relation established between age and CA rises from the progressive loss of angular momentum experienced by the star due to its magnetized wind, which reduces the stellar rotation. Therefore, roughly speaking, young stars are associated with intense chromospheric activity, whereas it decreases with stellar aging. However, some objects that show high kinematical components -- in turn, associated to older stars -- reveal similar CA to that of young ones; we call these objects chromospherically young and kinematically old (CYKOs). One hypothesis that could explain their occurrence is the merge of a short-period pair of stars, so that the angular momentum loss would be offset by progressive approximation until the merging -- whose outcome would be an chromospherically rejuvenated and active star with high kinematical components. We present 46 new candidates found by following a formalism previously used in literature. Some of them were observed in the 6708 A region with the 1.60 m coudé spectrograph from the Pico dos Dias observatory, Southern Brazil. Here we discuss our spectroscopic results with regard to the hypothesis that these are coalesced stars.

  • Multifractal manifestation of interplanetary magnetic field turbulence in a rope-rope magnetic reconnection event

    Submitted by: Fernando Marques
    Authors: Fernando F. Marques (1), Rodrigo A. Miranda(2) ((1) UnB - Mechanical Engineering Department, University of Brasília (UnB), Brasília, Brazil (2) UnB - Gama Campus, and Plasma Physics Laboratory, Institute of Physics, University of Brasília (UnB), Brasília, Brazil)
    We analyze the multifractal scaling of the modulus of the interplanetary magnetic field during a magnetic reconnection event. This event is characterized by three interplanetary magnetic flux ropes (IMFR), a bifurcated current sheet, and evidence of rope-rope magnetic reconnection. We quantify the degree of intermittency during the magnetic reconnection by computing the scaling exponents of the structure functions at each interval. The scaling exponents are then compared with the predictions obtained by the She-Lévêque model of intermittency in anisotropic magnetohydrodynamic turbulence. Magnetic reconnection occuring in the interface between two flux ropes can enhance the degree of intermittency and the degree of inhomogeneity related to the presence of sheet-like coherent structures. Our results can contribute to the understanding of the solar manifestation of the turbulent magnetic field in the heliosphere.

  • Coronal capabilities of the DKIST

    Submitted by: Valentin Martinez Pillet
    Authors: V. Martinez Pillet and the DKIST team (National Solar Observatory)
    With its 4m aperture and coronagraphic capabilities, the Daniel K Inouye Telescope (DKIST) will revolutionize solar physics. The 4m aperture enables unprecedented spatial resolutions and polarimetric (i.e., magnetic) sensitivities. DKIST will provide an excellent window into heretofore hardly accessible layers such as the solar chromosphere—the interface layer between the energy reservoir in the photosphere and the hot corona. The corona itself will regularly be observed with the telescope thanks to a set of aperture and focal plane occulters that minimize the direct light from the solar disk. The telescope will routinely make in the off-limb solar coronal physical conditions including the magnetic field, velocity flows, and chemical compositions. This new view of the Sun will provide highly improved understanding of the physics behind the processes that magnetically connect the Sun and the Earth, helping us to improve our modeling and predicting capabilities. In combination with the in-situ measurements of encounter missions such as Parker Solar Probe and Solar Orbiter, DKIST will enable a multi-messenger era for Solar Physics.

  • Integrated Science Investigation of the Sun (ISʘIS): Overview and Initial Results

    Submitted by: Ralph McNutt
    Authors: R. L. McNutt, Jr. (1,2), D.J. McComas (3), E. R. Christian (4), M. E. Wiedenbeck (5), N. A. Schwadron (6) ((1) Johns Hopkins University Applied Physics Laboratory, (2) On behalf of the PSP ISʘIS Team, (3) Princeton University, ( 4) NASA Goddard Space Flight Center, (5) Jet Propulsion Laboratory (6) University of New Hampshire)
    The Integrated Science Investigation of the Sun (ISʘIS) investigation on the Parker Solar Probe (PSP) consists of an instrument suite, which measures energetic particles over a very broad energy range, instrument and science operations, data processing, and scientific analysis. ISʘIS explores the mechanisms of energetic particles dynamics, including 1) Origins— defining the seed populations and physical conditions necessary for energetic particle acceleration; 2) Acceleration—determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and 3) Transport—revealing how energetic particles propagate from the corona out into the heliosphere. The ISʘIS suite comprises two instruments: the Energetic Particle Instrument - Low Energy (EPI-Lo) and the Energetic Particle Instrument - High Energy (EPI-Hi). EPI-Lo measures ions and ion composition from ∼20 keV/nucleon up to ~15 MeV total energy and electrons from ∼25 keV - 1 MeV. EPI-Hi measures ions from ∼1 - 200 MeV/nucleon and electrons from ∼0.5 - 6 MeV. Both instruments are designed to measure anisotropies in the particle distributions on the three-axis stabilized spacecraft: EPI-Lo comprises 80 apertures with fields-of-view (FoVs) that sample over nearly a complete hemisphere, while EPI-Hi combines three telescopes that together provide five large-FoV apertures. The ISʘIS Science Operations Center plans and executes commanding, receives and analyzes all ISʘIS data, and helps coordinate science observations and analyses with the rest of the PSP science investigations. Together, the unique observations of ISʘIS on PSP will enable the discovery, untangling, and understanding of the important physical processes that govern energetic particles in the innermost regions of our heliosphere. We summarize the investigation to date and provide a look at early ISʘIS data from the first perihelion pass of PSP in November 2018.

  • Characterizing Magnetic Activity as a Function of Mass and Rotation Period of Fully Convective M-dwarfs

    Submitted by: Amber Medina
    Authors: Amber Medina; David Charbonneau; Jennifer Winters; Jonathan Irwin (Harvard Smithsonian Center for Astrophysics)
    Main-sequence stars with masses less than 30% that of the Sun are fully convective and are the most abundant stars in the galaxy. The question of how fully convective stars generate their magnetic field is of intrinsic interest and also bears upon the habitability of their orbiting planets. We are undertaking a multi-epoch high-resolution spectroscopic volume-limited survey of stars with masses between 0.1-0.3 the solar value and within 15 parsecs. The stars in the sample are well characterized with accurate masses, radii, and photometric rotation periods from the MEarth Project. We present preliminary results on the variability of several indicators of magnetic activity, including H alpha, and how they relate to stellar properties such as rotation. We will compare the variability of magnetic activity indicators as a function of stellar rotation period, which will tell us how the magnetic field evolves throughout the lifetime of these fully convective stars and what implications that has for potentially habitable planets. This project was made possible through the support of a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This work was supported by grants from the National Science Foundation. A. M. is supported by an NSF Graduate Research Fellowship.

  • The effect of magnetic activity on radial velocities for different inclination angles: towards Earth 2.0

    Submitted by: Jorge Melendez
    Authors: Jorge Melendez (Universidade de Sao Paulo)
    Different stellar phenomena affect radial velocities (RV), imposing severe limitations for detection of small exoplanets, where the Keplerian signal could be smaller than the stellar jitter. In particular, the impact of magnetic activity on RV is hard to deal with, due to the changing distribution of stellar active regions, which are modulated by stellar rotation and activity cycles. As the amplitude of the RV-activity jitter is proportional to the stellar inclination angle, stars with low inclinations could be the best candidates for the detection of Earth analogs with small Keplerian signals (∼0.1 m/s). We plan to use ESPRESSO/VLT to study the relation between the RV-activity effect and inclination angle in solar twins, which could yield valuable targets in the quest for Earth 2.0.

  • Exploring Star-Planet Interactions with MHD Simulations

    Submitted by: Fabian Menezes
    Authors: Fabian Menezes, Adriana Valio (Centro de Rádio Astronomia e Astrofísica Mackenzie / Universidade Presbiteriana Mackenzie)
    Stars can strongly interact with their close-in planets through their magnetic field. The stellar magnetic field is the driver of activity in the star and can trigger energetic flares, coronal mass ejections and ionized wind. These phenomena may have an important impact on the magnetosphere and atmosphere of the orbiting planets. In this project for Foreign Student Program, we will focus on how stellar magnetic fields, their winds and flares impact close-in planets. Also, we will study how the magnetic reconnection between the planet and the star can trigger stellar activity. To accomplish that, we characterize spots (radius, intensity, and position) on the surface of some stars by fitting the small variations in the light curve of a star caused by the occultation of a spot during a planetary transit. Next, we develop stellar magnetic maps using the spots distribution on the stellar surface. From the spot temperatures we can determine its magnetic field intensity using the same relation of sunspots. This magnetic configuration is used as input for the three-dimensional magnetohydrodynamics numerical simulation of the stellar magnetic field. Moreover, the stellar interaction with a magnetized planet is investigated.

  • Evidence for a magnetic dynamo in hot Algols

    Submitted by: Ronald Mennickent
    Authors: Ronald Mennickent Cid (Universidad de Concepción)
    We review the evidence for a magnetic dynamo operating in some hot Algols showing non-orbital long photometric cycles. Signatures of chromospheric activity in the A/F/G giant stellar components of these binaries is summarized. We show the main characteristics of the "DPV phenomenon", this is the presence of an enigmatic photometric cycle lasting in average about 33 times the orbital period. This cycle is observed in the famous beta Lyrae, tens of Galactic binaries and hundreds of binaries in the SMC and LMC. We show how the Applegate's mechanism might be modulating the mass transfer rate through the inner Lagrangian point on the dynamo time-scale, producing epochs of larger luminosity, as recently suggested by Schleicher & Mennickent. Future research directions including polarimetric studies and models of the evolution of the internal structure of the donor star are discussed.

  • From the Sun to solar-type stars: radial velocity, photometry, astrometry and LogR’HK time series for late-F to early-K old stars

    Submitted by: Nadege Meunier
    Authors: N. Meunier, A.-M. Lagrange (Université Grenoble Alpes, CNRS, IPAG, France)
    Solar simulations and observations showed that the detection of Earth twins around Sun like stars should be very difficult if not impossible using radial velocity techniques, mostly due to the inhibition of the convective blueshift in plages. The Sun has proved to be a very useful reference case allowing to test processes, models, and analysis methods. The convective blueshift effect is however expected to decrease towards lower mass stars for example, as is the granulation signal, providing more suitable conditions to detect low mass planets. In addition to stellar intrinsic properties, stellar inclination also impacts significantly the time series at short and long time scales. It is therefore crucial to estimate precisely the effects of activity on exoplanet detectability using realistic time series. I will describe the basic processes at work and how we extended a realistic solar model of radial velocity, photometry, astrometry and LogR’HK time series: we built a coherent grid of stellar parameters covering a large range in effective temperature (K4-F6) and average activity level. I will present a few results concerning the impact of magnetic activity and supergranulation on Earth-mass planet detectability as a function of stellar type and other parameters. I will finally show how such realistic simulations can help interpreting photometric variability due to stellar activity, can help studying the impact of activity on astrometric exoplanet detection, and on the relationship between chromospheric emission and other time series.

  • Perspectives for asteroseismology of solar-like stars from TESS and PLATO

    Submitted by: Andrea Miglio
    Authors: Andrea Miglio (University of Birmingham)
    After a brief review on how CoRoT and Kepler opened the door to the study of stellar magnetic cycles using asteroseismology, I will discuss the opportunities given by, and limitations associated with, data from the ongoing TESS mission and the future ESA PLATO space telescope.

  • Intermittency and coherent structures in solar and stellar magnetic fields

    Submitted by: Rodrigo Miranda
    Authors: Miranda, R. A. (1), Chian, A. C.-L.(2,3), Rempel, E. L.(3,4), and Marques, F. (1) (1: University of Brasilia, Brasilia-DF, Brazil. 2: University of Adelaide, Adelaide-SA, Australia. 3: National Institute for Space Research, São José dos Campos-SP, Brazil. 4: Institute of Aeronautical Technology, São José dos Campos-SP, Brazil.)
    We show that on-off intermittency in solar and stellar magnetic fields can explain the random switching between periods of large and small amplitude variations observed in solar and stellar activities. The intermittency is a result of amplitude-phase synchronization in mutiscale interactions in magnetic field turbulence, and leads to the formation of magnetic and kinematic coherent structures in solar and stellar plasmas. Our results can improve our understanding of solar and stellar magnetic activities and the star-planet relation.

  • Relation between different magnetic photospheric and chromospheric activity phenomena on the young active star LQ Hya

    Submitted by: David Montes
    Authors: D. Montes, et al. (Dpto. Física de la Tierra y Astrofísica, Fac. C.C. Físicas, Universidad Complutense de Madrid, UCM)
    The association between different magnetic phenomena such as starspots in the photosphere and flares and prominences in the chromosphere is investigated using time-resolved high resolution spectroscopic observations of the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The chromospheric contribution of several activity indicators from the Ca II H & K to Ca II IRT lines has been determined using the spectral subtraction technique. Starspot filling factor and its longitudinal variation are obtained from Doppler Imaging and Titanium Oxide (TiO) band analysis. Observations are taken at different rotational phases and at different epochs during several years and it was possible to study in detail both rotational modulation and long-term variability.

  • The spatially constrained weak field approximation

    Submitted by: Roberta Morosin
    Authors: Roberta Morosin, Jaime de la Cruz Rodriguez (Stockholm University)
    By studying the magnetic topology and stratification of active regions on the Sun, we can take steps towards identifying chromospheric heating mechanisms and we can provide valuable constraints to theoreticians that must reproduce observations with their models. In the present project we propose to study the stratification of an active region on the Sun that has been observed in lines that sample different layers in the solar atmosphere, including the photosphere, the upper photosphere and the chromosphere. This project explores the idea of constraining the WFA along the spatial direction. The WFA is applied to observations by defining a merit penalty function and trying to minimize it.

  • How collisionless are solar wind electrons? Collisional and collisionless effects in the solar wind heat-flux transport

    Submitted by: Pablo Moya
    Authors: Pablo S Moya(1), Adolfo F Viñas(2), Rodrigo A López(3), Mark L Adrian(2), Javier Silva(1) ((1) Departamento de Física, Facultad de Ciencias, Universidad de Chile, Santiago, Chile; (2) NASA Goddard Space Flight Center, Greenbelt, MD USA; (3) Centre for mathematical Plasma Astrophysics (CmPA), KU Leuven, Belgium)
    Solar wind electrons are the main carriers of thermal conduction in the Heliosphere. Electron thermal conduction provides an important source of energy transport away from the Sun, and it is also the source for the electron heat-flux instability. The skewness of the electron distribution function can provide the free energy necessary to drive this micro-instability. Here, we analyze solar wind electrons in situ data at 1 AU, and show that collisional and collisionless effects can coexist and share dominance in the regulation of the heat-flux observed in situ in the solar wind, depending on the temperature radial profile and solar wind speed. Calculations of collisionless plasma instabilities driven by electrons modeled as a non-thermal skewed kappa distribution suggests that the heat-flux instability threshold marginally bounds solar wind heat-flux observations in fast speed streams. In contrast, for slow solar wind the collisional transport effects statistically increases and the heat-flux regulation is shared between collisional and collisionless effects.

  • Fractality of Magnetic Field Time Series in Magnetic Clouds

    Submitted by: Victor Munoz
    Authors: Víctor Muñoz, Macarena Domínguez, Simon Good (Departamento de Fisica, Facultad de Ciencias, Universidad de Chile; Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile; Department of Physics, University of Helsinki)
    In previous works, we have found that the fractal dimension is a useful way to characterize the state of a magnetized plasma, specially in the context of space physics phenomena, such as occurrence of geomagnetic storms[1], sunspot evolution[2] or dissipative events in models of MHD turbulence relevant to space plasmas.[3] In this work, we perform a similar analysis to study the time series of the magnetic field during magnetic clouds events, as observed by the MESSENGER spacecraft. It is found that the fractal dimension is able to characterize the cloud structure, distinguishing the various phases (the surrounding solar wind, sheath, and flux rope). By studying the dependence on the time delay to sample the data, results suggest that each phase has distinct multifractal behaviors. The time series analyzed correspond to the total magnetic field, as well as for each Cartesian coordinate as registered by the spacecraft. Some differences are found when individual coordinates are considered, but consistent results are recovered when axes are chosen according to a minimum variance criterion. One of the events was also observed by the STEREO-B spacecraft, which allows a preliminary study of the evolution of the fractal features of the cloud as it propagates away from the Sun. References [1] V. Muñoz, M. Domínguez, J. A. Valdivia, S. Good, G. Nigro, and V. Carbone, Nonlinear Proc. Geophys., 25, 2018, 207-216. [2] M. Domínguez, V. Muñoz, and J. A. Valdivia, J. Geophys. Res., 119, 2014, 10.1002/2013JA019433. [3] M. Domínguez, G. Nigro, V. Muñoz, and V. Carbone, Phys. Plasmas, 24, 2017, 072308.

  • The 3D structure of the penumbra at high resolution from the bottom of the photosphere to the middle chromosphere

    Submitted by: Mariart Murabito
    Authors: Murabito, M., Ermolli, I., Giorgi, F., Stangalini, M., Guglielmino, S. L., Jafarzadeh, S., Socas-Navarro, H., Romano, P., Zuccarello, F. (INAF-OAR,UNICT,UiO,IAC,INAF-OACT)
    Sunspots are the most prominent feature of the solar magnetism in the photosphere. Although they have been widely investigated in the past, their structure remains poorly understood. Indeed, due to limitations in observations and the complexity of the magnetic field estimation at chromospheric heights, the magnetic field structure of sunspot above the photosphere remains poorly understood. Improving the present knowledge of sunspot is important in solar and stellar physics, since spot generation is seen not only on the Sun but also on other solar-type stars. In this regard, we studied the large isolated sunspot (70’’x 80’’) located in the AR 12546 with spectro-polarimeteric measurements acquired at the Fe I 6173 nm and Ca II 8542 nm lines by the spectropolarimeter IBIS/DST, under excellent seeing conditions lasting more than three hours. Using the Non-LTE inversion code NICOLE we inverted both line measurements simultaneously, to retrieve the three-dimensional magnetic and thermal structure of the penumbral region from the bottom of the photosphere to the middle chromosphere. Analysis of data acquired at spectral ranges unexplored in previous studies allows us to show clear observational evidences of the spine and intra-spine structure of the magnetic field at chromopheric heights. In particular, we found a peak-to-peak variation of the magnetic field strength (never reported as yet) and inclination of about 200 G and 10° at chromopheric heights, respectively, and of about 300 G and 20° in the photosphere. We also investigated the structure of the magnetic field gradient in the penumbra along the vertical and azimuthal directions confirming previous analysis of data taken at the spectral region of the He I 1083 nm triplet.

  • Predicting the transit time of Halo-Coronal Mass Ejections during the Solar Cycle 24 using Machine Learning Algorithms

    Submitted by: Mohamed Nedal
    Authors: Mohamed Nedal, Ayman Mahrous, M.Youssef (Space Weather Monitoring Center (SWMC), Faculty of Science, Helwan University)
    Machine learning techniques have been widely used in several applications and recently they proved their validity and reliability in the field of space weather. In this work, the regression and classification techniques have been applied and the Artificial Neural Networks (ANN) have been employed to estimate the travel time of the Halo-Coronal Mass Ejections (HCME) during period 2009 - 2015. The list of events from (N Gopalswamy et al., 2010) with 176 CME-ICME pairs have been used as a training set, and the models have been tested on an independent testing set of 48 events obtained from (Michalek et al., 2004). Then, the models have been applied on 256 HCMEs obtained from SOHO/LASCO catalog. For the regression approach, the best result had RMSE = 17.63 hours. For the classification approach, the best result had a mean error of 4.5%. Using the ANN approach, the mean error was 13.14%.

  • FLUX EMERGENCE RATES OF SUNSPOTS

    Submitted by: Aimee Norton
    Authors: A.A. Norton, E.H. Jones, M.G. Linton, J.E. Leake (Stanford University, University of Southern Queensland, Naval Research Lab, NASA Goddard)
    Flux emergence rates of active regions observed using HMI/SDO are reported. Signed flux emergence rates for sunspots average 5 x 10^{19} Mx per hour. The observed rates from HMI are put into context with results previously reported from observations using various instruments and simulations. A clear trend is seen that larger flux regions emerge faster than smaller flux regions, with rates (dΦ/dt) scaling with total peak flux as a power law dΦ/dt ≈ Φ^{0.36}. Star spot emergence rates on Solar-type stars estimated with Kepler data are reported by Namekata et al. (2019) to follow a similar emergence rate and scaling law. Observed emergence rates may assist in constraining the choice of boundary and initial conditions in simulations which have already demonstrated that rates increase when a flux tube has higher buoyancy and twist, or is in the presence of a strong convective upflow.

  • The solar wind in time: 3D wind structure and radio emissions

    Submitted by: Dualta O Fionnagain
    Authors: D. Ó Fionnagáin, A. A. Vidotto (Trinity College Dublin)
    The solar wind permeates the environment around the Sun and up to the heliopause, encompassing our solar system and its planets. While we can directly measure the present-day solar wind, we have little evidence of what it was like over evolutionary timescales. To answer this question, we simulate the evolution of the solar wind along its main sequence lifetime. The evolution can be studied by using a sample of solar analogues at different ages as proxies for the solar wind at different evolutionary times. All these stars have observationally-reconstructed magnetic maps, which are incorporated in our 3D magnetohydrodynamic simulations of their winds. We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionary timescales, although they can vary in a magnetic cycle timescale. Stellar winds are known to emit radiation in the form of thermal bremsstrahlung in the radio spectrum. This radio emission can contain information on the mass-loss rates of these stars. To calculate the expected radio fluxes from these winds, we solve the radiative transfer equation numerically from first principles. We compute continuum spectra across the frequency range 100 MHz - 100 GHz and find maximum radio flux densities ranging from 0.05 - 2.2 μJy. We found that the best candidates for stellar wind observations in the radio regime are faster rotators within distances of 10 pc, such as κ1 Ceti (0.73 μJy) and χ1 Ori (2.2 μJy). These flux predictions provide a guide to observing solar-type stars across the frequency range 0.1 - 100 GHz in the future using the next generation of radio telescopes, such as the ngVLA and SKA.

  • Interferometric mapping the magnetic field in the remarkable W43 high-mass star-forming region

    Submitted by: Carlos Orquera-Rojas
    Authors: Carlos Orquera-Rojas, Paulo C. Cortés, Charles L. H. Hull (Pontificia Universidad Católica de Chile, National Radio Astronomy Observatory, Joint ALMA Office, National Astronomical Observatory of Japan)
    The role of the magnetic field in the formation of stars is not yet clear. Consequently, it is necessary to observe polarized dust emission to understand how the magnetic field interacts with the different variables (e.g., turbulence, infall) involved in the star formation process. Here we present the 1 mm ALMA observations of the polarized dust emission toward several of the most massive clumps in the high-mass star formation region W43. In this study, we map the morphology of the magnetic field, estimate the masses of the various clumps in each source, and estimate the magnetic field strength in each source using the Chandrasekhar-Fermi method. Indications have been found that the field is being dragged by gravity in some clumps; we have also observed differing levels of fragmentation in each source, yielding a wide range of masses and intensities for the clumps in each source.

  • Radiative MHD Simulations of Starspots

    Submitted by: Mayukh Panja
    Authors: Mayukh Panja, Robert Cameron, Sami K Solanki (Max Planck Institute for Solar System Research, Germany)
    We have performed the first-ever, realistic ab-initio simulations of the photospheric structure of starspots for a range of cool main-sequence stars, namely the spectral types M, K, G, and F. We use the radiative MHD code MURaM which includes radiative energy transfer and partial ionization. MURAM is so far the only radiative MHD code that has managed to compute complete sunspots with some semblance of realism. We explore several fundamental properties like umbral intensity contrast, temperature, and magnetic field strength as functions of spectral type. Our simulations show that there is an increase in spot contrast with increase in stellar surface temperature, which is consistent with observations. We will discuss the physical reasons for the existence of such a trend. In addition, we will examine the mechanisms responsible for the formation of penumbral filaments in cool starspots

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    Submitted by: Elielson Pereira
    Authors: - (-)
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  • The Dynamo-Wind Feedback Loop : Characterising how the solar wind varies along the 11-year solar cycle

    Submitted by: Barbara Perri
    Authors: Barbara Perri (1), Dr Allan Sacha Brun (1), Dr Victor Réville (2), Dr Antoine Strugarek (1) ((1) CEA Saclay AIM/IRFU/DAP/LDE3 (Paris France) and (2) EPSS, California, USA)
    Though generated deep inside the convection zone, the solar magnetic field has a direct impact on the Earth space environment via various mechanisms. It strongly modulates the solar wind in the whole heliosphere : observations have shown that the 11-year cycle created by the dynamo inside the Sun affects the latitudinal speed distribution of the solar wind over the years. However the wind also influences the topology of the coronal magnetic field by opening the magnetic field lines in the coronal holes, which can affect the inner magnetic field of the star by altering the dynamo boundary conditions. This coupling is especially difficult to model because it covers a large variety of spatio-temporal scales. Quasi-static studies have begun to help us unveil how the dynamical dynamo magnetic field shapes the wind. Nevertheless the full interplay between the solar dynamo and the solar wind still eludes our understanding. We use the compressible magnetohydrodynamical code PLUTO to compute simultaneously in 2.5D the generation and evolution of magnetic field inside the star via an alpha-omega dynamo process and the corresponding evolution of the corona over a solar-like 11-year cycle. A multi-layered boundary condition at the surface of the star connects the inner and outer stellar layers, allowing both to adapt and update in real time. We start during a minimum of activity, with a mostly dipolar magnetic field and an equatorial streamer. Transitioning to maximum of activity, the emergence of an opposite polarity toroidal field inside the star slowly changes the topology of the corona to quadrupolar, and leads to the opening of coronal holes at mid-latitudes and to the formation of pseudo-streamers. Finally the poloidal field is regenerated, the pseudo-streamers close and the corona comes back to a dipolar configuration. Our coupled dynamo-wind allow us to characterize how the solar wind conditions change as a function of the cycle phase, and also to quantify the evolution of the Alfvén surface, mass and angular momentum losses with the changing dynamo field. We further assess the impact of the solar wind on the dynamo itself by comparing our results with classical alpha-omega models with simple potential field boundary conditions.This gives us a new tool to better understand the Sun-Earth connection at various moments of the solar cycle in a space weather perspective and to eventually extend it to other star’s with different rotation and level of activity.

  • Deep polarimetry of a plage region

    Submitted by: Alexander Pietrow
    Authors: Alexander Pietrow, Dan Kiselman, Jaime de la Cruz Rodriguez (Stockholm University)
    Observationally deriving the connectivity of the magnetic field vector in solar plage regions, has the potential to increase MHD model realism. In order to measure the chromospheric magnetic fields over these regions deep polarimetry is required. To achieve this we have acquired high-cadence observations of a plage region at cos(theta) ~ 0.7 in Ca II 8542 with the CRISP instrument at the Swedish 1-m Solar Telescope (SST) on La Palma. We explore new ways of reconstructing the Stokes images to maximise the S/N while maintaining a high spatial resolution and, in Stokes I, a high temporal resolution. Using inversion methods we reconstruct the magnetic field vector in the chromosphere and present maps of the field above the plage and its connection to the surrounding regions.

  • Photometric variability and magnetic activity in young suns

    Submitted by: Geisa Ponte
    Authors: Geisa Ponte(1), Adriana Valio(1), Jorge Meléndez(2) ((1)Centro de Rádio-Astronomia e Astrofísica Mackenzie - Universidade Presbiteriana Mackenzie; (2)Instituto de Astronomia, Geofísica e Ciências Atmosféricas - Universidade de São Paulo)
    We investigate the impact of the chromospheric activity on precise 2 minute-cadence NASA/TESS lightcurves of a selected sample of young solar twins (with ages between 50 to 500 Myr). These stars were also monitored spectroscopically by the high-resolution planet hunter ESO/HARPS instrument over the course of, at least, one rotational period. We estimate photometric variability of lightcurves due to rotational modulations and explore its correlations with classical spectroscopic indicators of chromospheric activity (such as Ca II lines), ages and rotational periods. This valuable dataset will help us to understand the implications of magnetic activity variability in exoplanetary searches and its habitability and is an integrant part of a larger study aimed at characterizing comprehensively (photometrically and spectroscopically) the magnetic fields in young suns.

  • Progresses in shaping Fiber Arrayed Solar Optical Telescope(FASOT)

    Submitted by: Zhongquan Qu
    Authors: Z.Q. Qu (Yunnan Observatories, CAS)
    This talk introduces the progresses made in shaping Fiber Arrayed Solar Optical Telescope(FASOT) which is capable of real time spectro-imaging polarimetry of several magneto-sensitive spectral lines forming in the photosphere and chromosphere respectively. The information on stratification of the magnetic field as well as other physical parameters from the photosphere to chromosphere will be obtained simultaneously, and thus FASOT will become a powerful tool for the coming solar activity summit . The features and innovations of this telescope are detailed.

  • IRSOL spectropolarimetric observing programs and magnetic field diagnostics: recent advances.

    Submitted by: Renzo Ramelli
    Authors: R. Ramelli and the IRSOL observing team (IRSOL)
    Thanks to the excellent sensitvity of the ZIMPOL-III polarimeter, several interesting spectropolarimetric observing programs are carried out at the IRSOL observatory in Locarno (Switzerland) and in dedicated observing campaigns at GREGOR. The aim of this presentation is to give an overview on recent scientific results as well as on the improvements in the observing techniques and in the magnetic field diagnostics.

  • Parker Solar Probe: Mission Status and Outlook

    Submitted by: Nour E. Raouafi
    Authors: Nour E. Raouafi1; Stuart D. Bale2; Justin C. Kasper3; David J. McComas4; Russell A. Howard5; Marco Velli6; Arik Posner7; Rob Decker1; Aleida Higginson1 (1 Johns Hopkins University 2 Space Sciences Laboratory, University of California, 3 University of Michigan 4 Princeton University 5 U.S. Naval Research Laboratory 6 University of California, Los Angeles, 7 NASA Headquarters)
    The NASA Parker Solar Probe (PSP) spacecraft was launched on August 12, 2018 from Cape Canaveral Air Force Station, Florida. It is the first spacecraft to enter the atmosphere of a star, our Sun. The mission’s primary science goals are to determine the structure and dynamics of the Sun’s coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what mechanisms accelerate and transport energetic particles. Understanding these fundamental phenomena has been a top-priority science goal in astrophysics for over six decades. Parker Solar Probe is clearly a technologically challenging mission. It has to withstand the extreme heat and radiation environment of the solar atmosphere. Parker Solar Probe completed the first of twenty-four planned close encounters with the Sun between October 31 and November 11, 2018, all the while breaking records by being the fastest ever spacecraft and by making the closest ever approach to the Sun at 35 solar radii. Initial data from the mission have already been downlinked and Science Investigation Teams are expecting more data from this first perihelion in February-March. The second encounter with the Sun will be on March 30 – April 9, 2019. All the data from both encounters will be on the ground by the end of April. Solar Probe is primarily an exploration mission and the potential for discoveries is huge. The in-situ measurements made by FIELDS, SWEAP, and ISΘIS and white-light images from WISPR show plasma features that have not been observed before. We provide an overview on the status of the mission after two solar encounters, science data collected since launch, and the outlook of the mission based on past performance.

  • The Parker Solar Probe WISPR Instrument: Status and Observations

    Submitted by: Nour E. Raouafi
    Authors: Russell Howard (1), Angelos Vourlidas (2), Nour E. Raouafi (2), Robin Colaninno (1), Guillermo Stenborg (1), Phillip Hess (1), Paulett Liewer (3), Nathan Rich (1), and Hillary Dennison (1) ((1) U.S. Naval Research Laboratory, Space Science Division, United States, (2) Johns Hopkins University Applied Physics Laboratory, Laurel, United States, (3) Jet Propulsion Laboratory, Pasadena, United States)
    The PSP mission was launched Aug 12, 2018 into orbit about the Sun. In Oct/Nov it performed its first perihelion pass at 0.16 AU (36 solar radii). We present the plans and first observations of the corona for the WISPR instrument on the PSP mission. Observing the corona/solar wind from 0.25 AU to the ultimate perihelion distance of 0.04 AU is absolutely unique, but presents new challenges due to the rapidly changing heliocentric distance. WISPR, a heliospheric imager type of instrument, consists of two telescopes, which together observe in the spacecraft ram direction along the ecliptic plane from 13.5 - 108 deg from the Sun. This range of elongations encompasses the Thomson circle (the locus of points of maximum Thomson scattering efficiency) thereby transitioning from remote observations of structures close to the Sun to local observations of structures close to the spacecraft. Three different types of observations are envisioned: synoptic full field, partial field high cadence shock studies and partial field turbulence studies. The last one is a sequence of images at a 10-second cadence for which a power spectrum of intensity or electron density will be generated at selected heights in the corona, to see where wave energy is being deposited. In these preliminary images we anticipate that the view will be quite different as PSP plunges into the corona than the view from 1 AU. The spatial resolution will be greatly increased as we fly through the coronal structures and will reveal fine-scale details such as fluctuations in the plasma sheet, perhaps indicating individual flux tubes or magnetic islands or maybe something totally unexpected. The vantage points will remove a large fraction of the circumsolar dust contributing to the F-corona, perhaps also revealing the first dust to sublimate. To prepare for the mission, techniques have been developed to determine the background, track features that are moving through the field of view, among others. Due to the relative positions of PSP, Earth and the Sun, only a small fraction of the data has been received on ground, but WISPR has worked well through the first perihelion. We gratefully acknowledge support from the NASA Parker Solar Probe Project.

  • Detecting magnetic vortices and flux ropes in space and astrophysical plasmas

    Submitted by: Erico Luiz Rempel
    Authors: Erico L. Rempel, Tiago F. P. Gomes, Suzana de S. A. Silva, Abraham C.-L. Chian (Technological Institute of Aeronautics - ITA (Brazil) and University of Adelaide (Australia))
    Magnetic flux ropes are bundles of twisted magnetic field lines that occupy a (possibly deformed) cylindrical region. They are observed in many situations in space and astrophysical plasmas, such as coronal loops, coronal mass ejections and accretion disks. In two-dimensional flows, they degenerate into magnetic vortices, whose detection has challenged space scientists for years. In the present work, a new technique for detecting magnetic vortices is applied to magnetohydrodynamic simulations. The vortices are given by tubular level surfaces of the integrated averaged current deviation, the line integral of the normed difference of the local current from its spatial mean. This simple method is objective, i.e., invariant under space-dependent rotations and translations of the coordinate frame.

  • Statistical analysis of geomagnetic storms ocurrence rate and their relation with Solar cycle

    Submitted by: Paula Reyes
    Authors: P. Reyes[1], Pablo S. Moya[1], Victor A. Pinto [2] ([1] Universidad de Chile, [2] University of California Los Angeles)
    Geomagnetic storms are disturbances in the Earth’s magnetic field caused by interactions bet- ween magnetized plasma ejected from Sun and its magnetosphere. Intense magnetic storms are responsible of a wide range of damages over satellites, communi- cation systems and technological infrastructure in general. For this reason, the study of their oc- currence and intensity over time is relevant in space weather, in order to prevent and reduce their impact over modern technological infras- tructure. A Geomagnetic storm can be classified by their intensity through solar activity indexes. The Dis- turbance Storm Index (D st ) is an indicator of magnetic field produced by ring current near equa- tor, and large values are related to CME, solar flares and high-speed streams. The solar activity can be measured through Sunspots Number, and its periodic variation de- fines the Solar cycle that can be divided itself in four phases: minimum, ascending, maximum and descending. Large values of D st are often related to CME and solar flares during maximum phases and high-speed streams during declining phases of Solar Cycle. On this basis, the aim of this work is deepen on the statistical relation between occurrence ra- te of geomagnetic storms and Solar cycle, trea- ting a storm as a stochastic process, with a log- normal probability distribution function [1]. The data was obtained from D st time series between 1957-2018, where a storm is represented by its maximum intensity during main phase. Data we- re separated by Solar cycle, Solar cycle phases or both, and fitted through Maximum Likehood method. Finally, we calculated their median ra- te with 95 % confidence intervals using Bootstrap Method in order to find their occurrence in a pe- riod of 100 years. This results can be helpful to predict extreme events.

  • Potential zones in Peru for Astronomical Observatories

    Submitted by: Alexis Eder Rodríguez Quiroz
    Authors: Alexis Rodríguez Quiroz, Vanessa A. Navarrete Sotomayor - Agencia Espacial del Perú – CONIDA (Agencia Espacial del Perú – CONIDA)
    The growing interest in astronomical studies in Peru has generated the need to have its own Astronomical Observatories. This work collects the results of a previous study that shows that Peru has places with adequate conditions for astronomical observation and shows some recent results that will help identify potential areas for these purposes. Finally, the seasonal behavior of the chosen atmospheric parameters for one of the Peruvian zones will be presented, which will be compared with those of observatories in South America. The study conducted by CONIDA based on meteorological information collected over 40 years of the International Satellite Land-Surface Climatology Project (ISLSCP) project, the Surface Meteorology and Solar Energy (SSE) database in Peruvian territory concluded that in the south there are potential places to install astronomical observatories. This analysis considered parameters such as: lower cloud cover, humidity, precipitable water, dew point temperature and wind speed. With this background, it was decided to update this study, since at the moment we have access to data of atmospheric parameters of better spatial resolution, that is why we have used ERA-Interim data included in the years 2000 to 2016. This paper shows the average of each atmospheric parameter in Peru where the trend in each area can be visualized and potential zones identified.

  • Solar White Light Flares to understand the superflares occurring on G-stars

    Submitted by: Paolo Romano
    Authors: P. Romano (INAF - Catania Astrophysical Observatory)
    We analysed several extreme flares occurred on the Sun during the cycle 24 to interpret the observations of superflares discovered by the Kepler mission on G-stars in the optical continuum. Exploiting the high spatial resolution of the actual solar space-borne telescopes, we studied the magnetic field configuration of the active regions where some X-class flares, characterized by a significant emission at photospheric level, occurred. We used the photospheric vector magnetograms, taken by HMI onboard of the Solar Dynamics Observatory, as boundary conditions to reconstruct the non-linear force free coronal magnetic field before the flare occurrence. We found some common aspects in the magnetic field configurations which make the solar events as an interesting clue for the origin of white light flares in other stars. In particular, the detection of 3-D null points in the very low corona and the consequent occurrence of magnetic reconnection at low altitudes of the solar atmosphere seem to explain the optical continuum emission of those events. A similar configuration has been considered to describe the optical continuum source of superflares.

  • Dipolar stability in spherical simulations: the impact of an inner stable zone

    Submitted by: Bonnie Romano Zaire
    Authors: Bonnie R. Zaire; Laurene Jouve (IRAP)
    The stability of dipolar dynamos is known to depend on the system forcing. Fully convective dynamo simulations have shown that two dynamo regimes exist. One for moderate Rayleigh number, which results in strong dipolar fields, and another with more vigorous values that lead to complex magnetic field configurations. Here, we study the dipolar stability in a system with an inner stable zone, a configuration that resembles stars with radiative core. We present preliminary results of dynamo simulations using the Rayleigh number as a control parameter. The stiffness of the stable zone is accordingly varied to keep a constant ratio of the Brunt-Vaisala frequency to the angular velocity. In the full set of simulations we adopt the Ekman number equal to 10-4 and the Prandtl number equal to unity.

  • The rotation of low mass stars at 30 Myr in the cluster NGC 3766

    Submitted by: Julia Roquette
    Authors: J. Roquette, J. Bouvier, E. Moraux, H. Bouy, J. Irwin (University of Exeter, U.K.)
    Together with the stellar rotation, the spotted surfaces of low-mass magnetically active stars produce modulations in their brightness. These modulations can be resolved by photometric variability surveys, allowing direct measurements of stellar spin rates. In this poster, we present results of a multisite photometric survey dedicated to the measurement of spin rates in the 30 Myr cluster NGC 3766. Inside the framework of the Monitor Project, the cluster was monitored during 2014 in the i-band by the Wide Field Imager at the MPG/ESO 2.2-m telescope and by the 1m Swope Telescope. Data from Gaia-DR2 and griz photometry were used to identify cluster members. We present spin rates measured for ~200 cluster members. Inside the context of the rotational evolution of low mass stars during the pre Main Sequence, we discuss the main features in the spin rate distributions.

  • Solar Radius and Asphericities variations: outstanding unsolved points

    Submitted by: Jean Pierre Rozelot
    Authors: J.P. Rozelot, A. Kosovichev, A. Kilcik (UCA, Nice-F, NJST- USA, Akdeniz University, Antalya-TK)
    Since the highest Antiquity men have striven to measure the sizes of celestial bodies and among them the solar diameter. Its estimate is of importance as it serves as an astronomical standard. A change in its absolute measurement may change consequently the diameter of the stars, as for all of them, they are defined relative to that of the Sun. Moreover, if the solar diameter is slowly changing with time, it may result an impact on the inferred stellar structures. How the solar shape can be seen from the far outer space? Modern 3-D solar theories show that the near sub-solar surface can be modelized and is in rather good agreement with helioseismic observations as deduced from the Solar Dynamics Observatory (SDO) NASA satellite. An aspect of this helioseismic data analysis is the accurate determination of the mode parameters particularly at high degree (i.e. l up to 800), which leads to solar radius relative variations with the solar cycles modulation of amplitude. Therefore our star appears from the far space as a slowly pulsating star. Such findings can be transposed to exoplanets in their environment, placing the host star of an exoplanet as a variable star, a fact not considered up-to-now.

  • The Solar Clock

    Submitted by: Christopher Russell
    Authors: C. T. Russell(1), L.K. Jian(2), and J. G. Luhmann(3) ((1)University of California Los Angeles, Dept. of Earth, Planetary and Space Sciences, Los Angeles, CA, USA; (2) NASA Goddard Space Flight Center, Greenbelt, MD, USA; (3)University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, USA)
    A reliable time series of the sunspot number now exists that covers over 260 years. In this paper, we review aspects of the solar cycle that may lead to better understanding of the underlying physics of the solar dynamo that generates the magnetic field that in turn produces these sunspots. While the overarching goal of solar activity prediction has practical value for the prediction of space weather near Earth, the sunspot cycle also provides us insight into how the dynamo operates, which is of great scientific interest and debate. It is clear from visual examination that the maximum sunspot number, its rise time and decay times, and the sunspot cycle duration are all variable, but they are not random. These parameters remain within certain limits and exhibit certain classes of behavior. Herein, we review clues to the nature of the solar dynamo that are found in the sunspot numbers, in particular the rise times and rise rates of the sunspot number. We examine the assumption that the deep roots of the solar cycle lie inside the solar dynamo region and are controlled by a quite stable clock, finding a period of close to 11.05 yrs in the updated sunspot number record. We discuss the two classical sunspot cycle effects relating the maximum sunspot number to the rate of increase of the sunspot number and to the duration of the rising phase. Finally we consider the results in light of current explanations for the observed variations and their use in making solar cycle predictions.

  • Using the Solar Rotation software to determine the solar rotation period

    Submitted by: Alexandre Russi Junior
    Authors: Reinaldo Borges Júnior and Alexandre Russi Junior (Faculdade de Informática e Administração Paulista - FIAP)
    Sunspots are the most well-known phenomena of all time when you think about solar activity. This work analyses the results obtained of the sunspots observations as from the software Solar Rotation and uses these data for the calculation of the solar rotation period. The methodology adopted consisted of selecting photographs of the Sun on consecutive days of visible sunspots in the solar photosphere. Consequently, it was possible to calculate, in days, the rotation period of the Sun.

  • Imaging the Solar Corona during the March 2015 Solar Eclipse at Low Frequencies using LOFAR

    Submitted by: Aoife Maria Ryan
    Authors: Aoife M. Ryan[1,2,3], Peter T. Gallagher[3], Michiel A. Brentjens[4], Eoin P. Carley[3], Diana E. Morosan[5,1], Pietro Zucca[4], Christian Vocks[6], Max Gueret[1]. ([1]Trinity College Dublin, Ireland. [2]Astrotec Holding B.V., the Netherlands. [3]Dublin Institute for Advanced Studies, Ireland. [4]ASTRON, the Netherlands. [5]University of Helsinki, Finland. [6]Leibniz-Institut für Astrophysik, Potsdam, Germany.)
    Low frequency radio observations of the Sun during the solar eclipse of March 2015 have provided a means of determining how radio waves propagate through the corona. At low radio frequencies (≤ 400 MHz), scattering and refraction of these radio waves are thought to broaden sources to several arcminutes. The extent of these propagation effects can be constrained with the use of radio source size estimation. However, exactly how source size relates to scattering due to turbulence is still subject to investigation. Here, we use the LOw Frequency ARray (LOFAR) to observe the solar corona between 120 and 180 MHz during the solar eclipse of March 2015. We present an analysis detailing interferometric imaging of the radio corona using multi-frequency synthesis techniques. We determined source sizes associated with magnetically complex active regions in the corona which provides insight into the range of frequencies over which scattering effects dominate observed source sizes.

  • Data-constrained MHD Simulations of Solar Active Region Eruptions

    Submitted by: Antonia Savcheva
    Authors: Antonia Savcheva and Satoshi Inoue (Harvard-Smithsonian Center for Astrophysics [1], ISEE, Nagoya University [2])
    We present data-constrained MHD simulations of the CME eruptions of the February 2009 sigmoid. The initial conditions for the simulations have been produced with the flux rope insertion method, which creates highly observationally-constrained non-liner force-free models of the pre-flare states of the sigmoid for different times. The best-fit models in these cases, as has been shown before, are actually not force-free, but slightly unstable, which leads to eruptions in the MHD simulations of the different CMEs. We analyse the dynamics, the evolution of twist, and strong-to-weak shear transition in the (post-)flare loops. We perform topology analysis and identify the site of reconnection, the ribbon locations and motions, and dimmings size and evolution. We compare the properties of the different eruptions as the region evolves. All this is compared and validated by STEREO-B EUVI observations, for which, luckily the region is at disk center.

  • A spectroscopic analysis of the steady chromosphere of low-activity early-M dwarfs

    Submitted by: Gaetano Scandariato
    Authors: G. Scandariato (INAF-OACt)
    While most of the planets discovered so far have been found orbiting around solar-type stars, low-mass stars have recently been recognized as a "shortcut" to glance into an exo-life laboratory. Currently, stellar activity is one of the most limiting factors for achieving the precision required to detect Earth-twins via the radial velocity method. Understanding the chromospheres of M dwarfs is crucial to solve this problem. In this contribution I present the spectroscopic analysis of the quiet early-M dwarfs currently being monitored in the framework of the HADES (HArps-n red Dwarf Exoplanet Survey) radial velocity survey. The wavelength range covered by the spectra allows us to analyze simultaneously the CaII H&K doublet and the Balmer series, while the intensive follow up gives us a large number of spectra (up to ~100) for each targeted star. I present the study of the activity-rotation-stellar parameters and flux-flux relationships, and I also discuss the correlation of the CaII H&K and Hα fluxes at low activity levels and the evolution timescales of chromospheric active regions.

  • Comparing Zeeman-Doppler imaging and Zeeman broadening observations

    Submitted by: Victor See
    Authors: V. See, S. P. Matt, C. P. Folsom, S. Boro Saikia, J.-F. Donati, R. Fares, A. J. Finley, E. M. Hebrard, M. M. Jardine, S. V. Jeffers, L. T. Lehmann, S. C. Marsden, M. W. Mengel, J. Morin, P. Petit, A. A. Lidotto, I. A. Waite (P.I.: University of Exeter)
    Stellar magnetic fields are generally observed using one of two techniques. Zeeman-Doppler imaging can determine the geometry of the large-scale magnetic field but is insensitive to small-scale fields due to flux cancellation effects. Meanwhile, Zeeman broadening can determine the total unsigned flux, including that associated with small-scale structures, but cannot determine the field topology. These techniques are therefore complementary as neither can probe the full range of scales alone. I will present an analysis of a sample of stars that have been observed with both of these techniques. I show that Zeeman-Doppler imaging recovers a larger fraction of the photospheric magnetic flux in more active stars. I also estimate the fraction of the stellar surface covered in magnetic field as well as the fraction covered in field associated with open flux tubes, often called the filling factor and open filling factor respectively. This is done for a larger sample of stars that have been observed using Zeeman-Doppler imaging but not Zeeman broadening. I find indications that the most active stars may have smaller open filling factors than previously thought. I will discuss the implications of these results for stellar wind modelling.

  • Simulations of planetary transits of solar like stars at radio wavelengths

    Submitted by: Caius Selhorst
    Authors: C. L. Selhorst¹ and A. Valio (¹ NAT - Núcleo de Astrofísica Teórica, Universidade Cruzeiro do Sul, São Paulo, SP, Brazil)
    In this work we extend the analyses proposed by Selhorst et al. (2013) and simulate the quiet radio emission of solar like stars, that is, the reduction in flux caused by planetary transits. The stelar emission from submillimetric to metric wavelengths was simulated using the solar atmospheric model adjusted to reproduce the solar radio emission and considering bremsstrahlung as the main emission mechanism. To estimate the stellar flux reduction caused by the planetary transit, the planets were simulated as having a solid core (the emission assumed as a black body) and an atmosphere, which can be completely transparent at the smaller wavelengths or optically thick at the longer ones. The simulations were performed for several sizes of planets from super-Earths to hot Jupiters, and also distinct planetary atmospheric thickness.

  • Solar Polar Brightening and Radius at 100 and 230 GHz Observed by ALMA

    Submitted by: Caius Selhorst
    Authors: C. L. Selhorst¹, P. J. A. Simões, R. Brajša, A. Valio, C. G. Giménez de Castro, J. E. R. Costa, F. Menezes, J. P. Rozelot, A. S. Hales, K. Iwai, and S. White (¹ NAT - Núcleo de Astrofísica Teórica, Universidade Cruzeiro do Sul, São Paulo, SP, Brazil)
    Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some observations reported brightening values much smaller than the expected values obtained from the models, with discrepancies being particularly large at millimeter wavelengths. New clues to calibrate the atmospheric models can be obtained with the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) radio interferometer. In this work, we analyzed the lower limit of the polar brightening observed at 100 and 230 GHz by ALMA, during its Science Verification period, 2015 December 16-20. We find that the average polar intensity is higher than the disk intensity at 100 and 230 GHz, with larger brightness intensities at the South pole in eight of the nine maps analyzed. The observational results were compared with calculations of the millimetric limb brightnening emission for two semi-empirical atmospheric models, FAL- C (Fontenla et al. 1993) and SSC (Selhorst et al. 2005). Both models presented larger limb intensities than the averaged observed values. The intensities obtained with the SSC model were closer to the observations, with polar brightenings of 10.5% and 17.8% at 100 and 230 GHz, respectively. This discrepancy may be due to the presence of chromospheric features (like spicules) at regions close to the limb.

  • On Solar Jets: Driving Mechanism and Fine Structures

    Submitted by: Yuandeng Shen
    Authors: Yuandeng Shen (Yunnan Observatories, Chinese Academy of Sciences, China)
    Soar jets are omnipresent in the solar atmosphere. However, physical interpretations about their formation mechanism and fine structures are still open questions. By using the recent high resolution multi-wavelength observations taken by ground and space solar telescopes, we find that the eruptions of mini-filaments confined by the jet-base magnetic field are significant for explain many observing features in solar jets. In this talk, we will show that no matter the so-called standard jets or two-sided-loop jets are all originated from the eruption of mini-filaments, and the cool plasma flow in the jet spire is also form by the mini-filament eruption. In addition, solar jets can also launch large-scale coronal mass ejection. The physical mechanism and the relationship between solar jets and coronal mass ejections will also be introduced in this talk.

  • Magnetic loop asymmetry from flare observations of polarisation at millimeter wavelengths

    Submitted by: Douglas Silva
    Authors: Douglas F. Silva and Adriana Valio and Paulo Simões (CRAAM)
    To better understand the magnetic field configuration of flares, we have analysed the polarised millimetre-wave emission of the solar flare that occurred on November 5th, 2013. The measured right and left circularly polarised brightness temperatures of this flare at 45 and 90 GHz yield degrees of circular polarisation that reached up to 40%. Additional spectral data in microwaves from 1 - 15 GHz were obtained from the Radio Solar Telescope Network (RSTN). Images of hard X-rays by RHESSI were used to estimate the position where the flare occurred. The flux and polarisation radio spectra were fit using a model that simulates gyrosynchrotron emission in an inhomogeneous 3D magnetic field structure. The best fit yield an asymmetric magnetic loop, which was able to reproduce the degree of polarisation and radio spectrum observed fairly good. Therefore, the circular polarisation at 45 and 90 GHz may be explained by two sources located on the footpoints of an asymmetric magnetic loop with a very high field intensity. The results also showed a hard energy distribution of nonthermal electrons with a spectral index of 2,7.

  • Study of the relationship between the observations of the electron distributions in the solar wind and interplanetary magnetic fiels

    Submitted by: javier silva
    Authors: Javier Silva, Pablo Moya (Departamento de física de la Universidad de Chile)
    The space between the Sun and our planet is not empty. Corresponds to the expansion of the solar atmosphere, called solar wind, and is com- posed of a dimly weak plasma colisional compo- sed mainly of electrons and protons. Due to the lack of sufficient collisions, the function of elec- tron velocity distribution in the solar wind exhi- bits a variety of non-thermal characteristics that deviate from the thermal equilibrium. These de- viations from equilibrium provide a local source for electromagnetic fluctuations, intimately rela- ted to the shape of the distribution function, in- cluding the kinetic instabilities commonly obser- ved in whistler-cyclotron and firehose. Various space missions have been dedicated to the study in situ of the solar wind, with NA- SA’s Wind mission being one of the recent and successful. From their observations, various Phy- sics problems of weakly collisional plasmas have been able to be addressed experimentally, with great emphasis on populations of protons and ot- her minority ions. Showing, for example, that the magnetic fluctuations are bounded by the insta- bilities plasma kinetics in the temporal and spa- tial scales of the protons However, the physics of electrons has not been explored at the same level and there are several interesting questions still without a definitive answer. In this work we carry out a systematic analy- sis of the data of electrons and magnetic field measured by Wind between 1995 and 2001, stud- ying the relationship between the moments of the function of electron distribution (without separa- ting the data in different electronic components) and the properties of fluctuations magnetic fields, as well as the relationship of these quantities with kinetic instabilities in electronic scales. In parti- cular, We study the dependence of our statistical results on of solar wind speed, plasma collisiona- lity and the possible effect of the solar cycle. Our results could be relevant for the understanding of the physics of weakly collisional plasmas, and of particular interest in the prelude to the next space missions Parker Solar Probe and Solar Or- biter.

  • Semi-Empirical Model of Solar Wind

    Submitted by: Edward Sittler
    Authors: Edward C Sittler Jr (Self (work done without NASA funding))
    Using empirical models of the solar magnetic field and electron density using 2017 solar eclipse observations and boundary conditions established at 1 AU one can construct a 2D axisymmtric model of the solar wind flow. This would be the first step in developing 3D MHD models of the coronal expansion starting from the base of the corona to one AU.

  • Diagnostics of photospheric magnetic-fields on the Sun and stars

    Submitted by: Sami K. Solanki
    Authors: Sami K. Solanki (Max Planck Institute for Solar System Reseach)
    There are a number of methods available to measure the magnetic field from radiation. These include the Hanle effect, gyroresonant emission and Faraday rotation, but by far the most widely used, in particular in the photospheres of the Sun and stars, is the Zeeman effect. Therefore, diagnostics based on the Zeeman effect will lie at the core of this talk. These include inversion techniques, now widely used in solar physics, to deduce the height dependence of the magnetic vector as well as other atmospheric parameters. The Sun also allows time series of images to reveal the spatial distribution of the magnetic field and its evolution at increasingly higher resolution. On stars, the often small polarisation signals require techniques that enhance the S/N ratio. In addition, the spatial distribution of the field must be deduced from the rotational modulation of polarized line profiles and the field's evolution is accessible mainly on longer time scales. On both, the Sun and on stars, various shortcomings of the diagnostics, such as the 180 degree ambiguity in the deduced transverse field or the cancellation of the signal of opposite magnetic polarities within a spatial resolution element, set limits on the information that can be obtained about the magnetic field. Besides the diagnostics and their strengths, such limitations will also be discussed.

  • On the Role of Magnetic Fields in an Erupting Solar Filament

    Submitted by: Qiao Song
    Authors: Qiao Song1, Shuhong Yang2,3 and Jing-Song Wang1 (1. Key Laboratory of Space Weather, National Center for Space Weather, CMA, China; 2. CAS Key Laboratory of Solar Activity, NAOC, China; 3. School of Astronomy and Space Science, University of Chinese Academy of Sciences, China)
    At present, the 24th solar cycle is coming to its closing stage. The numbers of sunspots and flares have significantly decreased, but the solar quiescent filaments/prominences still erupt from time to time. The filament eruptions may lead to coronal mass ejection (CME), which is one of the main driving mechanisms of space weather events. It is believed that magnetic flux ropes play an important role for the erupting filaments and CMEs. This work analyses a slow and flareless CME event associated with an erupting quiescent filament. By using the extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, we trace the evolution of the filament, and present the details of the eruption and the manifestations of the magnetic fields in the low corona. Coronal cavity, horn-like structure, downflows and other fine structures are observed during the evolution. Some plasma blobs are moving upward along the filament and rotational motions occur at the foot of the filament. These results suggest the existence of the magnetic flux rope in the pre-eruption structures. A hot and long linear structure is also observed in EUV images during the eruption of the filament, which may indicate a current sheet. The eruption is without obvious X-ray enhancement but has growing post-eruption arcades. The magnetic energy of the eruption may be released via the ideal flux-rope instability and magnetic reconnection. Our study of this complex system may lead to a better understanding of the quiet Sun CME and its effect on the space weather forecast.

  • Distortion of the magnetic field in the Earth magnetosphere during strong geomagnetic storms

    Submitted by: Marina Stepanova
    Authors: M. Stepanova(1), E.E. Antonova(2), J.A. Valdivia(3) ((1) Physics Department, Universidad de Santiago de Chile, (2) Skobeltsyn Institute of Nuclear Physics Lomonosov Moscow State University, (3) Physics Department, Universidad de Chile)
    t is well known that magnetostatic equilibrium is crucial for stability of any plasma configuration. There is a lot of experimental evidence showing that balance of the total pressure in the magnetosphere is fulfilled. This enables us to use the MHD approach to describe global magnetospheric dynamics, including geomagnetic storms and substorms. At the same time, conservation of the plasma pressure along magnetic and current lines in magnetostatic equilibrium, allows the use of the pressure as a “natural tracer” to map one region into another. Using this technique, we conclude that most of the auroral oval is mapped to the cut-ring current (CRC) region, thereby explaining the ring-like shape of the auroral oval. Behavior of the plasma pressure in the magnetosphere during 1 July 2013 geomagnetic storm was studied by comparing the plasma pressure obtained from the precipitating ion fluxes, measured by the low-orbiting DMSP and POES data and the pressure obtained from the Van Allen Probes and THEMIS high-orbiting missions. It was found that the maximum of the plasma pressure and the most equatorial part of the westward auroral electrojet are located at the same L-shell as the seed population of electrons. Later, this leads to the formation of a new radiation belt at this location.

  • PEPSI: high-resolution spectropolarimetry with a 12m telescope. First ZDI results.

    Submitted by: Klaus G. Strassmeier
    Authors: K. G. Strassmeier, T. A. Carroll, S. Järvinen, I. V. Ilyin (AIP)
    The PEPSI polarimeter is entering its final commissioning at LBT in May this year. Earlier observations were on some interesting targets. Among our first result is that the surface temperature features on II Peg (a K2 subgiant in a binary) closely correlate with its magnetic field topology. We find a warm spot (350K warmer with respect to the effective temperature) of positive polarity and radial field density of 1.1 kG coexisting with a cool spot (780K cooler) of negative polarity of 2 kG. Several other cool features are reconstructed containing both polarities and with (radial) field densities of up to 2 kG. The largest cool spot is reconstructed with a temperature contrast of 550 K, an area of almost 10% of the visible hemisphere, and with a multipolar magnetic morphology. A meridional and an azimuthal component of the field of up to +/-500G is detected in two surface regions between spots with strong radial fields but different polarities. A force-free magnetic-field extrapolation suggests that the different polarities of cool spots and the positive polarity of warm spots are physically related through a system of coronal loops of typical height of 2 Rstar. While the H-alpha line core and its red-side wing exhibit variations throughout all rotational phases, a major increase of blue-shifted H-alpha emission was seen for the phases when the warm spot is approaching the stellar central meridian indicating high-velocity mass motion within its loop.

  • Detectability of magnetic star-planet interactions in realistic systems: the case of Kepler-78

    Submitted by: Antoine Strugarek
    Authors: A. Strugarek, A.S. Brun, C. Moutou, J.F. Donati (CEA Saclay Paris-Saclay, 91191 Gif-sur-Yvette Cedex, France)
    Close-in planets generally orbit in a sub-alfvénic stellar wind. The perturbations they excite in the stellar corona are able to travel upwind down to the stellar surface, and potentially induce observable phenomena. The effective connection between the planet and its host takes the form of two Alfvén wings. The stellar global magnetic field is at the heart of star-planet magnetic interaction: its strength sets the magnetic energy available for the interaction, its shape determines the connection path between the star and the planet, and its temporal modulation (e.g. magnetic cycles) is at the source of an on/off behavior of the magnetic interaction. I will briefly give an overview of our understanding of star-planet magnetic interactions and propose scaling laws for their amplitude. I will then present a specific study of the 3D star-planet magnetic interactions in the Kepler-78 system. Kepler-78 is a late G-type star around which a 1.86 Earth-mass planet orbit with an ultra-short period of 0.36 days. Based on this test case study, I will show that the detection of star-planet magnetic interactions generally requires a detailed knowledge of the stellar magnetic topology and amplitude. I will show that for favorable star-planet systems, the detection of star-planet magnetic interaction is theoretically possible with present telescope capabilities.

  • Big trouble in little Cen "The complex atmosphere and flare activity of Proxima and other M-dwarfs"

    Submitted by: Alejandro Suárez Mascareño
    Authors: A. Suárez Mascareño (Instituto de Astrofísica de Canarias)
    Stellar flares are explosive events on the surface of stars, believed to be due to the release of magnetic energy in magnetic reconnection events. These events are marked with a sudden increase of flux emission, followed by a gradual decay. This increase in flux takes place across a wide range of wavelengths, from radio to X-ray. Brightenings have been reported along the entire Main Sequence and in many stars off the Main Sequence. Some stars are decidedly young, others are in advanced stages of stellar evolution. It has been found that K and M stars will flare with greater relative amplitudes compared to those of earlier spectral type, with flare behaviour also changing within spectral types. Modern surveys, both ground- and space-based, provide quasi-continous observations that can reveal the flaring activity of many stars. Discoveries such as flare rates from inactive stars and “superflares” from field dwarfs have been enabled by surveys with long monitoring baselines and/or large spatial extents that reveal very rare events. M-dwarfs show some of the largest and most violent stellar flares of main sequence stars. In some cases, such as our neighbor Proxima, flares can make the star several magnitudes brighter for a brief period of time. Understanding the flaring activity of M-dwarfs can provide a unique look into their atmospheres and is also a key to properly establish the prospects of habitability on the most common stars in our galaxy.

  • Global dipole moment study using optimized surface flux transport model

    Submitted by: Mohammed Talafha
    Authors: Mohammed Talafha, Kristóf Petrovay (Dept. of Astronomy, Eötvös Loránd University)
    The importance of solar polar magnetic fields for the dynamo and for solar cycle forecasting has become increasingly clear in recent years. Polar fields are observed to be built up from active region trailing polarities by meridional flow advection and turbulent diffusion. The surface flux transport (SFT) models describing this process involve a number of free parameters and optional choices such as turbulent diffusivity, meridional flow amplitude or choice of meridional flow profile. In the past these choices were usually optimized to best reproduce the overall time-latitude pattern (butterfly diagram) of the magnetic field distribution. In this approach, mid-latitude features (plumes) are given great weight, while the smaller polar areas, observed less well due to perspective problems, have little influence. As a result, models optimized in this way often show significant disagreements with observations of the polar field, esp. regarding the timing of polar field reversals and maxima or latitudinal extent of the polar field concentration. We took the alternative approach of constraining SFT model parameters and assumptions by reducing the allowed parameter space to the domain where the phase of polar field variations and the latitudinal ex- tent of the polar magnetic cap agree with observational constraints. One important application of the result is considering the case when initially there is only a simple bipolar region, placed in some latitude, and run the SFT model with optimized parameters for some time until a dipolar field is formed, one can get the relation between the initial and final field, which can be introduced to the global dipole moment as a further factor as a function of latitude.

  • Temporal evolution of the velocity distribution in systems described by the Vlasov equation; Radiation Belts: Analytical and computational results.

    Submitted by: abiam tamburrini
    Authors: Abiam Tamburrini, Pablo Moya, Sergio Davis, Iván Gallo (Departamento de física de la Universidad de Chile(1), Comisión Chilena de Energía Nuclear(2).)
    Throughout our lives we have witnessed the interaction between the planet we inhabit and our star. The Earth's magnetosphere is one of its main consequences, originated by the interaction of the Earth's magnetic field and the solar wind, being highly sensitive to the activity of the sun, giving rise to many natural phenomena that intervene in our daily lives, such as geomagnetic storms, responsible for affecting navigation instruments. Many effects of this interaction are permantent, for example the radiation belts, composed of charged particles that were trapped in the magnetic field, whose variability in the outer belt is intimately related to solar activity and solar wind. Most of these phenomena are mediated by space plasmas, in particular the solar wind and regions of the magnetosphere, among others, are important examples of non-collisional plasmas, in which the presence of long-range interactions gives rise to stationary states (but not thermodynamic equilibrium) described by non-Maxwellian distributions such as the Kappa distribution. The dynamics of this system can be described from the point of view of nonequilibrium Statistical Mechanics, through the Vlasov equation [1]. This equation is the Liuoville theorem when the Hamiltonian describes an electromagnetic interaction. It is posible to derive relations for the expectation values of time-dependent observables from the Vlasov equation, using a classical analog of Ehrenfest theorem[2]. This work extends the previous study of classical Ehrenfest theorem in systems that satisfy the Vlasov equation to the evolution of velocity distributions, particularly in the Radiation Belt. Finally, the analytical results are compared with numerical results from computational simulations in the simple case of external and fixed electromagnetic field. Reference [1] P. Bellan, Fundamentals of Plasma Physics, Cambridge University Press (2006). [2] D. González, A. Tamburrini, S. Davis, and J. Jain. Journal of Physics: Conference Series, 2018.

  • Helioseismic perspectives on the solar dynamo

    Submitted by: Michael Thompson
    Authors: M. J. Thompson (NCAR / HAO)
    ------ATTENTION: It is with deep regret to share with you that Michael Thompson has recently passed away. If you would like to contact his family please email Kate Thompson (kate@katethompsontherapy.com) and Robin Thompson (robin.thompson1988@gmail.com). For NCAR related inquiries please contact Susan Chavez at chavez@ucar.edu and she can direct you to the appropriate POC.

  • Probing the Chromosphere-Corona Transition Region via UV Spectropolarimetry

    Submitted by: Javier Trujillo Bueno
    Authors: Javier Trujillo Bueno and the CLASP teams (IAC)
    Spectroscopic observations in ultraviolet (UV) spectral lines allow us to obtain empirical information on the thermal structure and dynamic behavior of the interface region between the chromosphere and corona of the Sun. Yet, to quantitatively explore the magnetic field and the geometrical complexity of the plasma in the upper solar chromosphere requires spectropolarimetry in magnetically sensitive UV spectral lines, such as hydrogen Lyman-alpha and the Mg II h & k lines. The sensitivity to the presence of magnetic fields in the upper solar chromosphere is caused mainly by the Hanle effect, which operates in the core of the linear polarization profiles produced by scattering processes, but recently we have learned that in such strong resonance lines other mechanisms can also introduce sensitivity to the presence of magnetic fields in lower atmospheric layers. The observation and modeling of the polarization produced in UV lines by the joint action of scattering processes and the Hanle and Zeeman effects are not easy, but the last few years have witnessed significant progress in this research field. On 3rd September 2015 an international team of scientists from USA, Japan and Europe carried out a challenging experiment with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP), which allowed to observe for the first time the linear polarization produced by scattering processes in the hydrogen Lyman-alpha line of the solar disk radiation. Radiative transfer modeling of these unprecedented data allows to constrain the magnetization and geometrical complexity of the chromosphere-corona transition region. We also inform about the second flight of CLASP, which will hopefully allow us to observe in 2019 the linear and circular polarization across the Mg II h & k lines in quiet and plage regions of the solar chromosphere.

  • Stellar magnetic fields from starspots characterisation from planetary transit mapping

    Submitted by: Adriana Valio
    Authors: Adriana Valio (1), Yuri Netto (1), S. M. Zaleski (2), Eduardo Spagiari (1) ((1) Center for Radio Astronomy and Astrophysics Mackenzie (CRAAM), Mackenzie Presbyterian University, Sao Paulo, Brazil; (2) University of Southern Queensland, Centre for Astrophysics, Toowoomba, Australia)
    During a transit of a planet in front of its host star, it may occult stellar features such as spots or faculae. This will cause small variations in the star light curve. Detailed analysis of these variations provides a wealth of information about starspot properties such as size, position, temperature (i.e. intensity), and magnetic field. This study is performed using a method that simulates the passage of a planet (dark disk) in front of a star with multiple spots of different sizes, intensities, and positions on its surface. A well known relation between temperature and magnetic field is established for sunspots. This same relation is applied for the spots detected on the transit light curves of other stars and thus their magnetic fields inferred. We present the results obtained from the analyses of the light curves of CoRoT-2, Kepler-17, Kepler-63 and Kepler-71.

  • MICRAS, MIchelson Colombian RAdiointerefometer System

    Submitted by: Santiago Vanegas
    Authors: Santiago Vanegas Pinzon, Giovanni Pinzon Estrada, Juan Carlos Martinez Oliveros (Radioastronomy, Sun)
    MICRAS : MIchelson Colombian RAdiointerefometer System Design, develop, set and operate instruments and Software tools to advance the knowledge of radio astronomy in Colombia represent a big effort and on-edge project to make investigations and labs for students to learn astronomy doing observational sessions, even with cloudy skies more than sixty percent of the nights of the year. Like thesis of master degree in astronomy, at the Observatorio Astronomico Nacional it develop and deploy an Radiotelescope Interferometer that uses techniques of adding two signal to obtain the total power of the two, this instrument looks like the original work presented by Michelson & Pease at 1921, and our work is based on the recent work of Jin Koda at Stony Brook University. The main objective is measure extended source like the Sun at 11 GHz, with a system of four flat mirrors to receive and reflect the signal. Two of those flat mirror are at the end of the guide with a distance between them called “Baseline”, each mirror receive the signal and reflect to the other two mirrors at the middle of the guide, an this reflect to a broadcast satellite parabolic dish where the signal are added. Moving the external mirrors we can change the baseline and the pattern of interference and the visibility to obtain measure the Sun’s diameter. It was built with a motorized pier to azimuth rotation and electric actuator to shift the inclination, this configuration able to find and locate easy the Sun and sweep the interferometer beam across the Sun disk during the laboratory session to obtain the interference pattern at several baselines. The scope of MICRAS makes possible the understanding of radioastronomy, and interferometry principles for university education. All of hardware develops and software tool are Open Source, and low cost and easy to achieve and replicate for other universities and research groups. Website: https://hackaday.io/project/27582-radiotelescope-interferometer-imfr11ghz

  • The impact of stellar magnetic activity and related phenomena on exoplanets

    Submitted by: Aline Vidotto
    Authors: Aline Vidotto (Trinity College Dublin)
    In this talk I will review some recent works on the magnetic activity of low-mass stars and the impact of activity-related phenomena on surrounding exoplanets. Because stellar magnetic fields drive the space weather of exoplanets, understanding the host star magnetism is a key ingredient for characterisation of exoplanetary environments. The extreme architecture of most of the known exoplanetary systems, in addition to the differences in magnetic properties of host stars compared to those of our Sun, can give rise to planet-star interactions that are not present in the solar system. These interactions can generate observable signatures, thus providing additional avenues for characterising exoplanetary systems. In this talk I will review some recent works on star-planet interactions and discuss their observability at different wavelengths (radio, IR, optical, UV, X-ray).

  • Evolution of slingshot prominences for different stellar massses

    Submitted by: Carolina Villarreal D'Angelo
    Authors: Carolina Villarreal D'Angelo (1), Moira Jardine(2), Colin Johnstone (3), Victor See (4) ((1)School of Physics,Trinity College Dublin; (2)SUPA, School of Physics and Astronomy, University of St Andrews; (3)Department of Astrophysics, University of Vienna; (4)University of Exeter, Department of Physics and Astronomy))
    Although the present-day Sun rotates too slowly to exhibit centrifugally-supported ``slingshot prominences'', at some time during its past it may have formed these clouds of cool gas and ejected them into the interplanetary medium. We determine the time period for this behaviour by using a rotation evolution code to derive the properties of the formation and ejection of slingshot prominences during the lifetime of a star similar to our Sun. The mass, mass loss rate and rate of ejection of these prominences are calculated using the analytical expression derived in our previous work. We find that for stars with an initial rotation rate larger than 4.6 times the solar rotation rate, about half of all solar mass stars, slingshot prominences will be present even after the star reaches the main sequence phase. In a fast rotator, this means that prominences can form until the star reaches ~ 800 Myr old. Our results also indicate that the mass and lifetime of this type of prominence have maximum values when the star reaches the ZAMS at an age of ~ 40 Myr for a solar mass star.

  • Star-planet interaction trough spectral lines

    Submitted by: Carolina Villarreal D'Angelo
    Authors: Carolina Villarreal D’Angelo & Aline A. Vidotto (School of Physics, Trinity College Dublin)
    The growth of spectroscopic observations of exoplanetary systems allows the possibility of testing theoretical models and studying the interaction that exoplanetary atmospheres have with the wind and the energetic photons from the star. In this work, we present a set of numerical 3D simulations of exoplanetary systems for which spectral lines observations of their evaporative atmospheres are available (including HD 209458b). Some of the most promising lines to study the star-planet interaction and the upper planetary atmosphere are Ly-alpha, H-alpha and the Helium lines. With our models, we can reconstruct the synthetic lines observed during transits and compare them with the real ones. Our results will help to constrain the planetary system parameters and to predict a positive or negative transit observation in a particular line.

  • SEARCHING THE CYCLE PERIOD IN CHROMOSPHERICALY ACTIVE STARS

    Submitted by: Fabricio Villegas
    Authors: F. Villegas, R. Mennickent (Universidad de Concepción)
    The detection and analysis of line emission of the CaII, H(396.8nm) and K(393.3nm) have confirmed the chromospheric activity of some single and binaries stars. This activity is associated to the presence of magnetic fields which in turn are produced by internal convective flows along with stellar rotation producing a long-term photometric cycle length related to the apparition and vanishing of superficial stellar spots. We present a photometric study of stars of the type RS CVn, Rotationally variable Star and BY Dra, that have shown evidence of chromospheric activity. We collected data with the TAROT telescope (0.5 m, CTIO) for a period of 3 years. To date we have collected around 6500 photometric data in filters C, g, r and i for 5 targets. The analysis of these measurements has allowed us to delimit periods of rotation (in the case of binary system assuming synchronous rotation). In addition, we have detected and measured the cycle length in some cases. This long-term monitoring campaign (still under execution) was possible thanks to CNTAC granted time. It allows us to complement previous investigations and in some cases to determine for the first time the presence of a long photometric cycle, contributing to complement the link between rotation and magnetic cycles of stars with low solar mass of spectral type K1III , K3III y K4V. Our results will help to understand the dynamo mechanism driving the long photometric cycles in these objects.

  • Dynamo transitions in simulations of Sun-like stars and understanding them

    Submitted by: Mariangela Viviani
    Authors: Viviani, M. [1], Käpylä, M. J. [1],[2], Warnecke, J. [1], Käpylä, P. J.[3],[2],[1], Rheinhardt, M.[2] ([1] Max Planck Institute for Solar System Research, Göttingen, Germany; [2] ReSoLVE Centre of Excellence, Department of Computer Science, Aalto University, Finland; [3] Georg-August-Universität Göttingen, Institut für Astrophysik, Göttingen, Germany)
    The large-scale magnetic activity of the Sun is cyclic, reverting the polarity of the magnetic field every 11 years, as a result of a dynamo operating in its convection zone. From photometric and chromospheric observations, we know that cyclic magnetic activity is not a prerogative of the Sun, but it is very common among stars with convective envelopes. Photometric observations [1] also show that younger and faster rotating stars present non- axisymmetric magnetic field, that is, the magnetic patches appear unevenly distributed in longitude and at high latitudes, in contrast to the Sun, where the appearance of sunspots is restricted to the equatorial belt, forming the so-called "butterfly diagram" in time, and does not present any particular dependence on longitude. The best way to understand the dynamos operating in stars and, in particular, the transition from axisymmetric magnetic fields to nonaxisymmetric ones is by means of numerical simulations of magnetohydrodynamics. In a recent numerical study on solar-like stars [2], where we increased the rotation rate of our models from the solar rotation rate, we were able to reproduce the axi-nonaxi transition. For the same rotation rate, we have also a transition in differential rotation: models above this threshold present solar-like differential rotation (fast equator and slower poles), while models rotating slower have anti-solar like differential rotation (faster poles and slow equator). This has been reported in many numerical studies before, but observations of stars with anti-solar differential rotation are still controversial. While oscillatory solutions have previously been found only for the solar-like rotation regime, our simulations show cycles in the anti-solar regime, too. Here we report on an attempt to understand these unexpected oscillatory solutions by mean-field theory, employing the test-field method. We calculated the turbulent transport coefficients using this method, and found out that they play a key role in the generation of the cyclic solutions. We then used the derived coefficients in a mean-field model and reproduced satisfactorily the DNS. As a consequence, we finally emphasize the importance of proper determination and modelling of turbulent processes to describe solar and stellar dynamos. References: [1] Lehtinen, J., Jetsu, L., Hackman, T., Kajatkari, P., and Henry, G. W., 2016, A& A, 588, A38. [2] Viviani, M., Warnecke, J., Käpylä, M. J., et al. 2018, A& A, 616, A160.

  • Measuring stellar magnetic fields with the Atacama Large Millimeter/Submillimeter Array

    Submitted by: Wouter Vlemmings
    Authors: Wouter Vlemmings (Chalmers University of Technology)
    I will present the polarisation capabilities of ALMA that enable the detection and mapping of magnetic fields around, specifically, evolved stars. Measurements of dust and molecular line polarisation are revealing large scale ordered magnetic fields around supergiants and asymptotic giant branch stars. At the same time, the highest angular resolution observations, reaching 1 au scales, are resolving the dynamics, temperatures, convection and shocks in the chromosphere/extended atmospheres of the nearby AGB stars. Zeeman splitting observations in the same regions will be able to directly combine magnetic field information with the other properties close to the photosphere.

  • Research and Development at CASSACA

    Submitted by: Zhong Wang
    Authors: Zhong Wang (CASSACA/NAOC)
    CASSACA is the astronomy research center set up by the Chinese National Astronomical Observatories (NAOC) in Chile, and its support extends to all areas of astronomy, including theory, observation, instrumentation and site survey. This is an introduction of the programs and research conducted at CASSACA, and we welcome international collaborations in any field of astronomical research, including solar physics and stellar magnetic fields.

  • Simulations of Flux Emergence in Cool Stars: The Role of Convection, Rotation, and Stellar Structure

    Submitted by: Maria Weber
    Authors: Maria A Weber (University of Chicago, Adler Planetarium)
    Establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos and starspot properties. Motivated by the fibril nature of solar surface magnetism, insight into the flux emergence process has been obtained by assuming the bundles of magnetic field giving rise to starspots consists partly of idealized, buoyantly rising thin flux tubes (TFTs). Here we present multiple sets of TFT simulations in rotating spherical shells of convection representative of cool stars. Our solar simulations reproduce sunspot observables such as low-latitude emergence, tilting action toward the equator following the Joy’s Law trend, and a phenomenon akin to active longitudes. We comment on the effect of rotation and convective flows (both local and mean) on the subsequent evolution of rising flux tubes in Suns rotating at three and five times the solar rate. Typically, rapid rotation deflects the flux tubes poleward, while strong radial flows distort the flux tube and differential rotation supplies it with added torque. Such TFT simulations share similarities, and a few differences, with buoyant magnetic structures that have recently been realized self-consistently in a unique set of convective dynamo simulations. We compare our TFT models in partially convective Suns to those of fully convective M dwarfs. In these simulations computed at the solar rotation rate, the expected starspot latitudes deviate from the solar trend, favoring significantly poleward latitudes unless the differential rotation is sufficiently prograde or the magnetic field is strongly super-equipartition. We also comment on the nature of flux emergence simulations in partially convective M dwarfs, focusing on the impact of convection and the formation of flux tubes either in the convectively stable tachocline region or the bulk of the convection zone. This work is a step toward linking magnetic flux emergence, convection, and dynamo action along the lower end of the main sequence.

  • Solar Cycle 25 Predictions

    Submitted by: Maria Weber
    Authors: Maria Weber, Lisa Upton, Douglas Biesecker, and the Solar Cycle 25 Prediction Panel (University of Chicago, Adler Planetarium)
    As the exceptionally weak Solar Cycle 24 comes to an end, we look to the future as we prepare for Solar Cycle 25. This past March, NOAA and NASA convened the first meeting of the Solar Cycle 25 Prediction Panel. The panel conducted a survey of forecasts for the amplitude and timing of Solar Cycle 25 in order to obtain and recommend a consensus forecast. This forecast will serve as the official Solar Cycle 25 Prediction for NOAA, NASA, and the International Space Environment Services (ISES). In addition to the amplitude and timing of Solar Cycle 25, the panel will address complicating issues, such as the impact of the revised sunspot number (SSN) on the predictions and the potential for hemispheric asymmetry of Solar Cycle 25. We will present a summary of the first Solar Cycle 25 Prediction Panel meeting and any consensus that we have achieved on Solar Cycle 25.

  • Observing the Sun with the Atacama Large Millimeter/submillimeter Array – From continuum to magnetic fields

    Submitted by: Sven Wedemeyer
    Authors: Sven Wedemeyer (Rosseland Centre for Solar Physics, University of Oslo)
    The Atacama Large Millimeter/submillimeter Array offers regular observations of our Sun since 2016. After an extended period of further developing and optimizing the post-processing procedures, first scientific results are now produced. While the first observing cycles mostly provided mosaics and time series of continuum brightness temperature maps with a cadence of 1-2s, additional receiver bands and polarization capabilities will be offered in the future. Currently, polarization capabilities are offered for selected receiver bands but not yet for solar observing. An overview of the recent development, first scientific results and potential of solar magnetic field measurements with ALMA will be presented.

  • Evidence of Magnetic Star Planet Interaction

    Submitted by: Scott Wolk
    Authors: Scott Wolk (Harvard-Smithsonian Center for Astrophysics)
    Soon after the discovery of hot Jupiters, it was suspected that interaction of these massive bodies with their host stars could give rise to observable signals. I discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays. It is now clear that Hot Jupiters can significantly impact the activity of their host stars through tidal and magnetic interaction, leading to either increased or decreased stellar activity - depending on the internal structure of the host star and the properties of the hosted planet. We provide several examples of these interactions. In HD 189733, the strongest X-ray flares are preferentially seen in a very restricted range of planetary phases. Hot Jupiters, can also obscure the X-ray signal during planetary transits. Observations of this phenomena have led to the discovery of a thin upper atmospheres in HD 189733A. On the other hand, WASP-18 - a young F6 star with a massive hot Jupiter, shows no signs of activity in X-rays or UV. In this system, tidal SPI between the star and the very close-in and massive planet appears to disrupt the surface shear layer and thus nullify the stellar activity.

  • Diagnosing coronal magnetic fields with radio imaging-spectroscopy technique

    Submitted by: Yihua Yan
    Authors: Yihua Yan, Baolin Tan, Victor Melnikov and MUSER Team (CAS Key Lab of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences)
    Mingantu Spectral Radioheliograph (MUSER) is a radio synthesis imaging telescope, dedicated to observe the Sun, operating on multiple frequencies in dm to cm range. The ability of MUSER to get images and measure Stokes I and V parameters simultaneously at many frequencies in a wide band is of fundamental importance. It allows one to approach/solve such important problems as measuring the strength, geometry and dynamics of magnetic field at coronal heights. Here we consider some of the recently developed radio physics methods to be used for solving the problems. These methods allow us to obtain information that is unattainable in other areas of the electromagnetic spectrum. The emission mechanism corresponding to different regions in the solar corona is in general different: bremsstrahlung emission in the quiet corona; cyclotron (gyro-resonance) and gyro-synchrotron emission in the active regions; and synchrotron, plasma emission, and/or electron cyclotron maser in the flaring regions. Therefore, the coronal magnetic field diagnostics is a most complicated work including determining exactly physical partitions in source regions, identifying emission mechanism, applying diagnosing functions, etc. Here we present the initial coronal magnetic field diagnosing results from MUSER observations.

  • Trigger mechanisms of the major solar flares

    Submitted by: Shuhong Yang
    Authors: Shuhong Yang ((1) CAS Key Lab of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences; (2) School of Astronomy and Space Science, University of Chinese Academy of Sciences)
    Solar flares, suddenly releasing a large amount of magnetic energy, are one of the most energetic phenomena on the Sun. For the major flares (M- and X-class flares), there exit strong-gradient polarity-inversion lines in the pre-flare photospheric magnetograms. Some parameters (e.g., shear angle, electric current, free energy) are used to measure the magnetic non-potentiality of active regions, and the kernels of major flares are found to coincide with the highly non-potential regions. Magnetic emergence and cancellation, shearing motion, and sunspot rotation observed in the photosphere are deemed to play an important role in the energy buildup and flare trigger. Solar active region 12673 produced 4 X-class, 27 M-class, and numerous lower-class flares during its passage across the visible solar disk in 2017 September, and the X9.3 flare on September 6 is the largest one in solar cycle 24. According to the newly proposed block-induced eruption model, because of the standing of a pre-existing sunspot, the block-induced complex structures built the flare-productive active region and the X9.3 flare was triggered by an erupting filament due to the kink instability.

  • On the properties of magnetic peculiar B, A, and F-type stars

    Submitted by: Kutluay Yuce
    Authors: Kutluay YUCE (1), Saul J. ADELMAN (2), Diana M. Pyper (3) ((1)Ankara University (Ankara), (2)The Citadel (Charleston), (3) Nevada University (Las Vegas))
    We are completing the analysis of the remaining unpublished uvby photometry from the Four College Automated Photometric Telescope of the magnetic CP stars corresponding to B, A, and F main sequence stars. It operated for 22.3 years before failure in the late Fall of 2012. We review our analyses of magnetic CP stars using Stromgren uvby photometry especially during the past ten years. including the periods, standard deviations, and light variability in the u, v, b and y bandpasses bands for defining two physically different groups called hot and cool mCP stars. Summarizing the FCAPT and other extensive data sets should lead to improvements in our knowledge of the photometric variabilities of magnetic CP stars and lead to improved test the theory of chemically peculiar stars.

  • Why magnetic reconnection easily occur?

    Submitted by: Jun Zhang
    Authors: Jun Zhang, Yijun Hou, Xiaohong Li, & Sihui Zhong (National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049)
    Magnetic reconnection is an important mechanism for energy transformation in the solar atmosphere. Observations show that magnetic reconnection easily occurs in the solar photosphere, chromosphere, and corona. Under laboratory conditions, we can also handily reappear magnetic reconnection. To answer the question "why magnetic reconnection easily occur", we suggest for the first time that the magnetic field may possess some special properties.

  • Multiple Magnetic Reconnections Driven by a Large-scale Magnetic Flux Rope

    Submitted by: Guiping Zhou
    Authors: G. P. Zhou, C. M. Tan, Y. N. Su, C. L. Shen, B. L. Tan, C. L. Jin, and J. X. Wang (Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Science)
    Magnetic flux ropes (MFRs), as the most probable core structure of solar eruptive activity, remain mysterious on their origination, magnetic environment, and erupting mechanisms. Here, we newly identify a large-scale hot channel MFR, named “MFR3”, that connects an anti-Hale active region (AR) 11429 and a normal AR 11430 on 2012 March 7 based on multi-wavelength observations. An oscillation is first detected at the top of MFR3 during 00:10–00:30 UT as triggered by an X5.4 flare-related eruption of an MFR (named “MFR1” here) in AR 11429. Then, after a quiet period of ∼20 minutes at around 00:52 UT, external magnetic reconnection (EMR) occurred above MFR3 manifested by not only bidirectional outflow in extreme ultraviolet images, but also microwave quasi-periodic pulsation in broadband radio spectral observations for the first time. With the occurrence of EMR, the large-scale MFR3 quickly erupted at 01:01 UT and triggered an X1.3 flare, which is related to the eruption of the other MFR (named “MFR2” here) in AR 11429 at 01:05 UT. The erupting MFR3 and MFR2 appeared successively in the same associated halo coronal mass ejection (CME) as two different core structures. The identification of the large-scale MFR3 between two separated ARs and its complex activity may shed new light on our understanding of the initiation mechanism of a CME. Further work should lay emphasis on how a large-scale MFR3 forms in the solar atmosphere.

  • Evolution of multifractality in solar magnetograms

    Submitted by: Tomas Zurita
    Authors: Tomas Zurita and Victor Muñoz (University of Chile)
    Various measures of complexity may yield relevant ways to study the complexity in the dyna- mics of magnetized plasma. In a previous study, we calculated the fractal dimension of solar magnetograms, taken from the Michelson Doppler Imager (MDI) Daily Magnetic Field Synoptic Data . These are averages of several observations collected over a solar rotation, and represent the magnetic field strength on the solar surface. We used a box-counting algorithm to calculate the fractal dimension of solar magnetograms along the complete 23rd solar cycle, finding a good correlation with solar activity as measured by sunspot number. In the current work, we extend the analysis by calculating Renyi multifractal spectrum, leading to an estimation of the degree of multifractality, and its evolution along the solar cycle.