Solar and Stellar Magnetism

    General
    Description

    Magnetic fields are at the base of star formation and stellar structure and evolution. When stars are born, magnetic fields brake the rotation during the collapse of the mollecular cloud. In the end of the life of a star, magnetic fields can play a key role in the form of the strong winds that lead to the last stages of stellar evolution. During the whole adult life of a star, magnetic fields are the origin of stellar activity. Our Sun has magnetic fields that give rise to such spectacular activity that impacts the climate on Earth. The magnetic activity in other stars is, in some cases, of orders of magnitude more intense than the solar one, influencing – often drastically – the transport of chemical species and angular momentum, as well as affecting the possible planetary systems around them.

    The aim of this project is the study of the diverse manifestations of the magnetic field that can be observed in the solar atmosphere and in other stars. These include distinct structures as sunspots, weak quiet-sun fields or chromospheric and coronal features such as filaments and prominences. The following research topics have been gradually faced:

    Solar magnetism

    1. Structure and evolution of Sunspot magnetic fields.

    2. Structure and evolution of quiet Sun magnetic fields.

    3. Structure and evolution of the magnetism of the chromosphere and of chromospheric strcutures (promiences, spicules,...)

    4. Structure and evolution or coronal loops.

    5. Structure and evolution of the Sun's global field. Studies of the activity cycle.

    6. Empirical study of propagation of magnetohydrodynamic waves in magnetic structures.

    7. Empirical study of energy transfer mechanisms related with the heating of the external atmospheric layers.

    8. Empirical study of the influence of partial ionisation in the dynamics of the solar atmosphere.

    9. Participation in the European Solar Telescope project.

    Stellar magnetism

    1. Development of numerical tools to diagnose stellar magnetic fields, both in the surface and in the chromsphere.

    2. Study of magnetic fields in stellar prominences.

    3. Study of the role of magnetic fields in the late stages of stellar evolution.

    Principal investigator
    Project staff
    1. Spiral waves in sunspots: They have been interpreted as magnetoacoustic waves propagating from the interior to the atmosphere following the direction of the magnetic field. We have characterized the magnetic field topology, dismissing the twist of the field lines as the cause of the spiral shape (Felipe et al. 2019).
    2. Magnetic response to umbral flashes: Simultaneous spectropolarimetric observations of the chromospheric He I 10830 and Ca II 8542 lines have been used to estimate the fluctuations of the magnetic field associated to shock waves. The shocks cause expansion of the magnetic field lines (Houston et al. 2018, including A. Asensio Ramos).

    Related publications

    • Inference of electric currents in the solar photosphere

      Context. Despite their importance, routine and direct measurements of electric currents, j, in the solar atmosphere have generally not been possible. Aims: We aim at demonstrating the capabilities of a newly developed method for determining electric currents in the solar photosphere. Methods: We employ three-dimensional radiative magneto

      Pastor Yabar, A. et al.

      Advertised on:

      12
      2021
    • Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region

      In order to investigate the relation between magnetic structures and the signatures of heating in plage regions, we observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation

      Anan, Tetsu et al.

      Advertised on:

      11
      2021
    • Multiple Stokes I inversions for inferring magnetic fields in the spectral range around Cr I 5782 Å

      Aims: In this work, we explore the spectral window containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I, Fe I, Mn I, and Si I

      Kuckein, C. et al.

      Advertised on:

      9
      2021
    • Large-amplitude longitudinal oscillations in solar prominences simulated with different resolutions

      Context. Large-amplitude longitudinal oscillations (LALOs) in solar prominences have been widely studied in recent decades. However, their damping and amplification mechanisms are not well understood. Aims: In this study, we investigate the attenuation and amplification of LALOs using high-resolution numerical simulations with progressively

      Liakh, V. et al.

      Advertised on:

      10
      2021
    • Diagnostic capabilities of spectropolarimetric observations for understanding solar phenomena. I. Zeeman-sensitive photospheric lines

      Future ground-based telescopes will expand our capabilities for simultaneous multi-line polarimetric observations in a wide range of wavelengths, from the near-ultraviolet to the near-infrared. This creates a strong demand to compare candidate spectral lines to establish a guideline of the lines that are most appropriate for each observation target

      Quintero Noda, C. et al.

      Advertised on:

      8
      2021
    • Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation

      Context. With the advent of next generation high resolution telescopes, our understanding of how the magnetic field is organized in the internetwork (IN) photosphere is likely to advance significantly. Aims: We aim to evaluate the extent to which we can retrieve accurate information about the magnetic vector in the IN photosphere using inversion

      Campbell, R. J. et al.

      Advertised on:

      10
      2021
    • Limitations of the Ca II 8542 Å Line for the Determination of Magnetic Field Oscillations

      Chromospheric umbral oscillations produce periodic brightenings in the core of some spectral lines, known as umbral flashes. They are also accompanied by fluctuations in velocity, temperature, and, according to several recent works, magnetic field. In this study, we aim to ascertain the accuracy of the magnetic field determined from inversions of

      Felipe, Tobias et al.

      Advertised on:

      9
      2021
    • Performance of solar far-side active region neural detection

      Context. Far-side helioseismology is a technique used to infer the presence of active regions in the far hemisphere of the Sun based on the interpretation of oscillations measured in the near hemisphere. A neural network has recently been developed to improve the sensitivity of the seismic maps to the presence of far-side active regions. Aims: Our

      Broock, E. G. et al.

      Advertised on:

      8
      2021
    • Exploring the Sun's upper atmosphere with neural networks: Reversed patterns and the hot wall effect

      We have developed an inversion procedure designed for high-resolution solar spectro-polarimeters, such as those of Hinode and the DKIST. The procedure is based on artificial neural networks trained with profiles generated from random atmospheric stratifications for a high generalization capability. When applied to Hinode data, we find a hot fine

      Socas-Navarro, H. et al.

      Advertised on:

      8
      2021
    • Two-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread. II. Effects of collisionality

      Solar prominences are formed by partially ionized plasma with inter-particle collision frequencies generally warranting magnetohydrodynamic treatment. In this work we explore the dynamical impacts and observable signatures of two-fluid effects in the parameter regimes when ion-neutral collisions do not fully couple the neutral and charged fluids

      Popescu Braileanu, B. et al.

      Advertised on:

      6
      2021
    • Bayesian Evidence for a Nonlinear Damping Model for Coronal Loop Oscillations

      Recent observational and theoretical studies indicate that the damping of solar coronal loop oscillations depends on the oscillation amplitude. We consider two mechanisms: linear resonant absorption and a nonlinear damping model. We confront theoretical predictions from these models with observed data in the plane of observables defined by the

      Arregui, Iñigo

      Advertised on:

      7
      2021
    • Machine learning initialization to accelerate Stokes profile inversions

      Context. At present, an exponential growth in scientific data from current and upcoming solar observatories is expected. Most of the data consist of high spatial and temporal resolution cubes of Stokes profiles taken in both local thermodynamic equilibrium (LTE) and non-LTE spectral lines. The analysis of such solar observations requires complex

      Gafeira, R. et al.

      Advertised on:

      7
      2021
    • Mapping the Hidden Magnetic Field of the Quiet Sun

      The Sun is the only star where we can resolve the intricate magnetism that all convective stars harbor. Yet, more than 99% of its visible surface along the solar cycle (the so-called quiet Sun) is filled with a tangled, unresolved magnetism. These "hidden" fields are thought to store enough magnetic energy to play a role in the heating of the Sun's

      Trelles Arjona, J. C. et al.

      Advertised on:

      7
      2021
    • Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

      The importance of the chromosphere in the mass and energy transport within the solar atmosphere is now widely recognized. This review discusses the physics of magnetohydrodynamic waves and instabilities in large-scale chromospheric structures as well as in magnetic flux tubes. We highlight a number of key observational aspects that have helped our

      Srivastava, A. K. et al.

      Advertised on:

      6
      2021
    • Simulations of the Biermann battery mechanism in two-fluid partially ionised plasmas

      Context. In the absence of an initial seed, the Biermann battery term of a non-ideal induction equation acts as a source that generates weak magnetic fields. These fields are then amplified via a dynamo mechanism. The Kelvin-Helmholtz instability is a fluid phenomenon that takes place in many astrophysical scenarios and can trigger the action of

      Martínez-Gómez, D. et al.

      Advertised on:

      6
      2021
    • Probing Uncertainties in Diagnostics of a Synthetic Chromosphere

      Effective spectroscopic diagnostics rely on the ability to convert a particular flux measurement into a physical interpretation. Knowledge of uncertainty is a central component of diagnostics. We present data from a simulated solar-like chromosphere, where we have addressed the question of whether degeneracy is a problem in mapping from a non-LTE

      Schmit, Don et al.

      Advertised on:

      5
      2021
    • Rubidium abundances in solar metallicity stars

      Context. Rubidium is one of the few elements produced by the neutron capture s- and r-processes in almost equal proportions. Recently, a Rb deficiency ([Rb/Fe] < 0.0), amounting to a factor of about two with respect to the Sun, has been found in M dwarfs of near-solar metallicity. This stands in contrast to the close-to-solar [Sr, Zr/Fe] ratios

      Abia, C. et al.

      Advertised on:

      4
      2021
    • Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)

      The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary

      Rast, Mark P. et al.

      Advertised on:

      4
      2021
    • Combining magneto-hydrostatic constraints with Stokes profiles inversions. II. Application to Hinode/SP observations

      Context. Inversion techniques applied to the radiative transfer equation for polarized light are capable of inferring the physical parameters in the solar atmosphere (temperature T, magnetic field B, and line-of-sight velocity vlos) from observations of the Stokes vector (i.e., spectropolarimetric observations) in spectral lines. Inferences are

      Borrero, J. M. et al.

      Advertised on:

      3
      2021
    • Empirical determination of atomic line parameters of the 1.5 μm spectral region

      Context. Both the quality and amount of astrophysical data are steadily increasing over time owing to the improvement of telescopes and their instruments. This requires corresponding evolution of the techniques used for obtaining and analyzing the resulting data. The infrared spectral range at 1.56 μm usually observed by the GRegor Infrared

      Trelles Arjona, J. C. et al.

      Advertised on:

      4
      2021

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