Magnetism, Polarization and Radiative Transfer in Astrophysics

    General
    Description

    Magnetic fields pervade all astrophysical plasmas and govern most of the variability in the Universe at intermediate time scales. They are present in stars across the whole Hertzsprung-Russell diagram, in galaxies, and even perhaps in the intergalactic medium. Polarized light provides the most reliable source of information at our disposal for the remote sensing of astrophysical magnetic fields, including those on the Sun. In particular, the diagnostics of solar and stellar magnetic fields requires the measurement and physical interpretation of polarization signatures in spectral lines, which are induced by various physical mechanisms taking place at the atomic level. In addition to the familiar Zeeman effect, polarization can also be generated by various other physical processes, such as atomic level polarization induced by anisotropic pumping mechanisms, quantum interference between fine-structured or hyperfine-structured energy levels, the Hanle effect, etc. Interestingly, the polarization produced by such mechanisms is sensitive to the physical conditions of the astrophysical plasma under consideration and, in particular, to the presence of magnetic fields in a parameter domain that goes from field intensities as small as 1 micro-G to many thousands of Gauss.

    The main objective of this project is to explore in depth the physics and origin of polarized radiation in astrophysical plasmas as well as its diagnostic use for understanding cosmical magnetic fields, with emphasis on the magnetism of the extended solar atmosphere. Our investigations deal with:

    -the theoretical understanding of relevant polarization physics, which requires new insights into the quantum theory of polarized light scattering in the presence of magnetic and electric fields.

    -the development of plasma diagnostic tools for the investigation of astrophysical magnetic fields, with emphasis on the magnetism of the extended solar atmosphere, circumstellar envelopes and planetary nebulae.

    -spectropolarimetric observations and their physical interpretation.

    -radiative transfer in three-dimensional models of stellar atmospheres, resulting from magneto-hydrodynamical simulations.

    -atomic and molecular spectroscopy and spectro-polarimetry, with applications in several fields of astrophysics.

    This research project is formed by a group of scientists convinced of the importance of complementing theoretical and observational investigations in order to face some of the present challenges of 21st century Astrophysics.

    Principal investigator
    1. We applied deep learning techniques to the analysis of observations. Using convolutional neural networks, we developed techniques for the deconvolution of observational data. These techniques were also used to accelerate the deconvolution process of ground-based observations, achieving a cadence of around a hundred images processed per second.
    2. We developed an inference technique based on bayesian statistics in order to interpret the observations provided by the CLASP international experiment. By parametrizing a state-of-the-art magneto-hydrodynamical model of the solar atmosphere, we found that the geometrical complexity of the transition region must be much more complex than the one provided by the model.
    3. We solved the problem of polarized radiation transfer in magneto-convection simulations that account for small-scale dynamo action for the Sr I line at 460.7 nm. We found that the model with most of the convection zone magnetized close to the equipartition and a surface mean field strength of 170G is compatible with the available observations.
    4. We studied the magnetic sensitivity of the Ca I line at 422.7nm. The linear polarization at the core is sensitive to the Hanle effect, while the linear polarization in the wings is sensitive to the magneto-optical effects, as a consequence of the newly found effect resulting from the joint action of partial redistribution and the Zeeman effects.
    5. We studied the formation of the H-alpha, Mg II h-k, and Ca II H-K and 845.2nm in a model atmosphere of a flaring bipolar active region, solving the radiation transfer problem taking into account partial redistribution in full 3D geometry and out of local thermodynamical equilibrium. We succeeded in reproducing common observational features of such flaring regions.

    Related publications

    • Magnetic imaging of the outer solar atmosphere (MImOSA) Unlocking the driver of the dynamics in the upper solar atmosphere

      The magnetic activity of the Sun directly impacts the Earth and human life. Likewise, other stars will have an impact on the habitability of planets orbiting these host stars. The lack of information on the magnetic field in the higher atmospheric layers hampers our progress in understanding solar magnetic activity. Overcoming this limitation would

      H. Peter, et al.

      Advertised on:

      2021
    • Mapping solar magnetic fields from the photosphere to the base of the corona

      Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet we remain blind to its main driver, the magnetic field. Here we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg II

      McKenzie, David E. et al.

      Advertised on:

      2
      2021
    • Modeling the scattering polarization of the solar Ca I 4227 Å line with angle-dependent partial frequency redistribution

      Context. The correct modeling of the scattering polarization signals observed in several strong resonance lines requires taking partial frequency redistribution (PRD) phenomena into account. Modeling scattering polarization with PRD effects is very computationally demanding and the simplifying angle-averaged (AA) approximation is therefore commonly

      Janett, Gioele et al.

      Advertised on:

      11
      2021
    • Polarization of the Lyα Lines of H I and He II as a Tool for Exploring the Solar Corona

      The near-Earth space weather is driven by the quick release of magnetic free energy in the solar corona. Probing this extremely hot and rarified region of the extended solar atmosphere requires modeling the polarization of forbidden and permitted coronal lines. To this end, it is important to develop efficient codes to calculate the Stokes profiles

      Hebbur Dayananda, Supriya et al.

      Advertised on:

      10
      2021
    • Newly formed downflow lanes in exploding granules in the solar photosphere

      Context. Exploding granules have drawn renewed interest because of their interaction with the magnetic field (either emerging or already present). Especially the newly forming downflow lanes developing in their centre seem to be eligible candidates for the intensification of magnetic fields. We analyse spectroscopic data from two different

      Ellwarth, M. et al.

      Advertised on:

      9
      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
    • On the (Mis)Interpretation of the Scattering Polarization Signatures in the Ca II 8542 Å Line through Spectral Line Inversions

      Scattering polarization tends to dominate the linear polarization signals of the Ca II 8542 Å line in weakly magnetized areas (B ≲ 100 G), especially when the observing geometry is close to the limb. In this paper, we evaluate the degree of applicability of existing non-LTE spectral line inversion codes (which assume that the spectral line

      Centeno, Rebecca et al.

      Advertised on:

      9
      2021
    • Solving the Paradox of the Solar Sodium D<SUB>1</SUB> Line Polarization

      Twenty-five years ago, enigmatic linear polarization signals were discovered in the core of the sodium D1 line. The only explanation that could be found implied that the solar chromosphere is practically unmagnetized, in contradiction with other evidences. This opened a paradox that has challenged physicists for many years. Here we present its

      Alsina Ballester, Ernest et al.

      Advertised on:

      8
      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
    • Naked emergence of an anti-Hale active region. I. Overall evolution and magnetic properties

      Aims: In order to understand the emergence of the active region, we investigate the emerging process and magnetic properties of a naked anti-Hale active region during the period between August 24 to 25, 2018. Methods: Using the data from Helioseismic and Magnetic Imager on board the Soar Dynamic Observatory and the New Vacuum Solar Telescope, we

      Wang, Jincheng 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
    • 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
    • Long Characteristics versus Short Characteristics in 3D Radiative Transfer Simulations of Polarized Radiation

      We compare maps of scattering polarization signals obtained from three-dimensional (3D) radiation transfer calculations in a magnetoconvection model of the solar atmosphere using formal solvers based on the "short characteristics" (SC) and the "long characteristics" (LC) methods. The SC method requires less computational work, but it is known to

      de Vicente, A. 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
    • Emergence of Internetwork Magnetic Fields through the Solar Atmosphere

      Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they emerge all over the Sun, these small-scale fields bring a substantial amount of flux, and therefore energy, to the solar surface. Because of this, IN fields are crucial for understanding the quiet Sun

      Gošić, M. et al.

      Advertised on:

      4
      2021
    • Evaluating the Reliability of a Simple Method to Map the Magnetic Field Azimuth in the Solar Chromosphere

      The Zeeman effect is of limited utility for probing the magnetism of the quiet solar chromosphere. The Hanle effect in some spectral lines is sensitive to such magnetism, but the interpretation of the scattering polarization signals requires taking into account that the chromospheric plasma is highly inhomogeneous and dynamic (i.e., that the

      Jurčák, Jan et al.

      Advertised on:

      4
      2021
    • The Impact of Limited Time Resolution on the Forward-scattering Polarization in the Solar Sr I 4607 Å Line

      Theoretical investigations predicted that high spatiotemporal resolution observations in the Sr I 4607 Å line must show a conspicuous scattering polarization pattern at the solar disk center, which encodes information on the unresolved magnetism of the intergranular photospheric plasma. Here we present a study of the impact of limited time

      del Pino Alemán, T. et al.

      Advertised on:

      3
      2021
    • Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere

      Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves. Aims: We aim

      Campbell, R. J. et al.

      Advertised on:

      3
      2021

    Related talks

    No related talks were found.

    Related conferences

    No related conferences were found.