Start year
2007
Organizational Unit
Organizing institutions
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.
Members
Principal investigator
Tanausú del
Pino Alemán
Project staff
Andrés
Asensio Ramos
Javier
Trujillo Bueno
Héctor David
Socas Navarro
Nikola
Vitas
Andrii
Sukhorukov
Ángel Manuel de
Vicente Garrido
Fernando
Moreno Insertis
Supriya
Hebbur Dayananda
Sara
Esteban Pozuelo
Edgar Samuel
Carlín Ramírez
Collaborators
Carlos
Allende Prieto
Íñigo
Arregui Uribe-Echevarría
Cristina
Ramos Almeida
Dr.
M. Bianda
Dr.
R. Ramelli
Dr.
L. Belluzzi
Dr.
R. Casini
Dr.
R. Centeno
Dr.
J. de la Cruz
Dr.
N. Shchukina
Dr.
H. Uitenbroek
Dr.
D. Mckenzie
Dr.
R. Ishikawa
Basilio
Ruiz Cobo
María Jesús
Martínez González
Results
- 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.
- 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.
- 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.
- 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.
- 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.
Scientific activity
Related publications
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Bayesian Stokes inversion with normalizing flowsStokes inversion techniques are very powerful methods for obtaining information on the thermodynamic and magnetic properties of solar and stellar atmospheres. In recent years, highly sophisticated inversion codes have been developed that are now routinely applied to spectro-polarimetric observations. Most of these inversion codes are designed toDíaz Baso, C. J. et al.
Advertised on:
32022 -
Novel framework for the three-dimensional NLTE inverse problemThe inversion of spectropolarimetric observations of the solar upper atmosphere is one of the most challenging goals in solar physics. If we account for all relevant ingredients of the spectral line formation process, such as the three-dimensional (3D) radiative transfer out of local thermodynamic equilibrium (NLTE), the task becomes extremelyŠtěpán, Jiří et al.
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32022 -
Approximate Bayesian neural Doppler imagingAims: The non-uniform surface temperature distribution of rotating active stars is routinely mapped with the Doppler imaging technique. Inhomogeneities in the surface produce features in high-resolution spectroscopic observations that shift in wavelength because of the Doppler effect, depending on their position on the visible hemisphere. TheAsensio Ramos, A. et al.
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22022 -
Convolutional Neural Networks and Stokes Response FunctionsIn this work, we study the information content learned by a convolutional neural network (CNN) when trained to carry out the inverse mapping between a database of synthetic Ca II intensity spectra and the vertical stratification of the temperature of the atmospheres used to generate such spectra. In particular, we evaluate the ability of the neuralCenteno, Rebecca et al.
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22022 -
Empirical relations between the intensities of Lyman lines of H and He<SUP>+</SUP>Context. Empirical relations between major UV and extreme UV spectral lines are one of the inputs for models of chromospheric and coronal spectral radiances and irradiances. They are also needed for the interpretation of some of the observations of the Solar Orbiter mission. Aims: We aim to determine an empirical relation between the intensities ofGordino, M. et al.
Advertised on:
12022 -
The polarization angle in the wings of Ca I 4227: A new observable for diagnosing unresolved photospheric magnetic fieldsContext. When observed in quiet regions close to the solar limb, many strong resonance lines show conspicuous linear polarization signals, produced by scattering processes (i.e., scattering polarization), with extended wing lobes. Recent studies indicate that, contrary to what was previously believed, the wing lobes are sensitive to the presence ofCapozzi, Emilia et al.
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12022 -
Magnetic imaging of the outer solar atmosphere (MImOSA)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 wouldH. Peter, et al.
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122022 -
Mapping solar magnetic fields from the photosphere to the base of the coronaRoutine 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 IIMcKenzie, David E. et al.
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22021 -
Modeling the scattering polarization of the solar Ca I 4227 Å line with angle-dependent partial frequency redistributionContext. 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 commonlyJanett, Gioele et al.
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112021 -
Polarization of the Lyα Lines of H I and He II as a Tool for Exploring the Solar CoronaThe 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 profilesHebbur Dayananda, Supriya et al.
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102021 -
Newly formed downflow lanes in exploding granules in the solar photosphereContext. 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 differentEllwarth, M. et al.
Advertised on:
92021 -
Limitations of the Ca II 8542 Å Line for the Determination of Magnetic Field OscillationsChromospheric 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 ofFelipe, Tobias et al.
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92021 -
On the (Mis)Interpretation of the Scattering Polarization Signatures in the Ca II 8542 Å Line through Spectral Line InversionsScattering 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 lineCenteno, Rebecca et al.
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92021 -
Solving the Paradox of the Solar Sodium D<SUB>1</SUB> Line PolarizationTwenty-five years ago, enigmatic linear polarization signals were discovered in the core of the sodium D 1 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 itsAlsina Ballester, Ernest et al.
Advertised on:
82021 -
Performance of solar far-side active region neural detectionContext. 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: OurBroock, E. G. et al.
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82021 -
Naked emergence of an anti-Hale active region. I. Overall evolution and magnetic propertiesAims: 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, weWang, Jincheng et al.
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82021 -
Exploring the Sun's upper atmosphere with neural networks: Reversed patterns and the hot wall effectWe 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 fineSocas-Navarro, H. et al.
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82021 -
Two-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread. II. Effects of collisionalitySolar 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 fluidsPopescu Braileanu, B. et al.
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62021 -
Probing Uncertainties in Diagnostics of a Synthetic ChromosphereEffective 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-LTESchmit, Don et al.
Advertised on:
52021 -
Long Characteristics versus Short Characteristics in 3D Radiative Transfer Simulations of Polarized RadiationWe 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 tode Vicente, A. et al.
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52021
