General
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
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
-
Are solar chromospheric fibrils tracing the magnetic field?
Fibrils are thin elongated features visible in the solar chromosphere in and around magnetized regions. Because of their visual appearance, they have been traditionally considered a tracer of the magnetic field lines. For the first time, we challenge that notion by comparing their orientation to that of the magnetic field, obtained via high
de la Cruz Rodríguez, J. et al.Advertised on:
32011 -
A New Approach to the Solar Oxygen Abundance Problem
In this work we present new data that sets strong constraints on the solar oxygen abundance. Our approach, based on the analysis of spectropolarimetric observations, is almost model-independent and therefore extremely robust. The asymmetry of the Stokes V profile of the 6300 Å [O I] and Ni I blend is used as an indicator of the relative abundances
Centeno, R. et al.Advertised on:
72008 -
A high-resolution three-dimensional model of the solar photosphere derived from Hinode observations
A new three-dimensional model of the solar photosphere is presented in this paper and made publicly available to the community. This model has the peculiarity of having been obtained by inverting spectro-polarimetric observations, rather than by using numerical radiation hydrodynamical simulations. The data used here are from the spectro
Socas-Navarro, H.Advertised on:
52011 -
Polar Field Reversal Observations with Hinode
We have been monitoring yearly variation in the Sun's polar magnetic fields with the Solar Optical Telescope aboard Hinode to record their evolution and expected reversal near the solar maximum. All magnetic patches in the magnetic flux maps are automatically identified to obtain the number density and magnetic flux density as a function of the
Shiota, D. et al.Advertised on:
72012 -
Pervasive Linear Polarization Signals in the Quiet Sun
This paper investigates the distribution of linear polarization signals in the quiet-Sun internetwork using ultra-deep spectropolarimetric data. We reduce the noise of the observations as much as is feasible by adding single-slit measurements of the Zeeman-sensitive Fe I 630 nm lines taken by the Hinode spectropolarimeter. The integrated Stokes
Bellot Rubio, L. R. et al.Advertised on:
92012 -
On the Distribution of Quiet-Sun Magnetic Fields at Different Heliocentric Angles
This paper presents results from the analysis of high signal-to-noise ratio spectropolarimetric data taken at four heliocentric angles in quiet-Sun internetwork regions with the Hinode satellite. First, we find that the total circular and total linear polarization signals vary with heliocentric angle, at least for fields with large polarization
Orozco-Suárez, D. et al.Advertised on:
22012 -
Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals
We present results from the analysis of Fe I 630 nm measurements of the quiet Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets with noise levels of 1.2 × 10-3 and 3 × 10-4 are employed. We determine the distribution of field strengths and inclinations by inverting the two observations with a Milne-Eddington model
Orozco-Suárez, D. et al.Advertised on:
52012 -
Resonance scattering polarization in the magnetosphere of Mercury
The conditions of the exosphere of Mercury constitute a prime example of a magnetosphere subject to space weather. We aim at improving the diagnostic of the physical conditions of Na atoms in the exosphere of Mercury, with particular emphasis in the possibility of inferring the magnetic field through polarimetry of the Na D emission lines. We
López Ariste, A. et al.Advertised on:
82012 -
Polarimetric Diagnostics of Unresolved Chromospheric Magnetic Fields
For about a decade, spectropolarimetry of He I λ10830 has been applied to the magnetic diagnostics of the solar chromosphere. This resonance line is very versatile as it is visible both on disk and in off-limb structures, and it has a good sensitivity to both the weak-field Hanle effect and the strong-field Zeeman effect. Recent observations of an
Casini, R. et al.Advertised on:
82009 -
Magnetic field strength of active region filaments
Aims: We study the vector magnetic field of a filament observed over a compact active region neutral line. Methods: Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 Å spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and
Kuckein, C. et al.Advertised on:
72009 -
Wave Propagation and Shock Formation in Different Magnetic Structures
Velocity oscillations "measured" simultaneously at the photosphere and the chromosphere—from time series of spectropolarimetric data in the 10830 Å region—of different solar magnetic features allow us to study the properties of wave propagation as a function of the magnetic flux of the structure (i.e., two different-sized sunspots, a tiny pore, and
Centeno, R. et al.Advertised on:
22009 -
Three-dimensional Radiative Transfer Modeling of the Polarization of the Sun's Continuous Spectrum
Polarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the three-dimensional (3D) structure of the solar atmosphere. Here we formulate and solve the 3D radiative transfer problem of the linear polarization of the solar continuous radiation, which is
Trujillo Bueno, Javier et al.Advertised on:
42009 -
The Influence of Coronal EUV Irradiance on the Emission in the He I 10830 Å and D3 Multiplets
Two of the most attractive spectral windows for spectropolarimetric investigations of the physical properties of the plasma structures in the solar chromosphere and corona are the ones provided by the spectral lines of the He I 10830 and 5876 Å (or D3) multiplets, whose polarization signals are sensitive to the Hanle and Zeeman effects. However, in
Centeno, R. et al.Advertised on:
42008 -
The Hanle Effect of the Hydrogen Lyα Line for Probing the Magnetism of the Solar Transition Region
We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the linear-polarization signals produced by scattering processes in the hydrogen Lyα line of the solar transition region. To this end, we have calculated the atomic-level polarization (population imbalances and quantum coherences) induced by anisotropic
Trujillo-Bueno, J. et al.Advertised on:
92011 -
Solar magnetism eXplorer (SolmeX). Exploring the magnetic field in the upper atmosphere of our closest star
The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar corona—that can also affect life on
Peter, Hardi et al.Advertised on:
42012 -
Scattering Polarization of the Ca II IR Triplet for Probing the Quiet Solar Chromosphere
The chromosphere of the quiet Sun is a very important stellar atmospheric region whose thermal and magnetic structure we need to decipher in order to unlock new discoveries in solar and stellar physics. To this end, we need to identify and exploit observables sensitive to weak magnetic fields (B
Manso-Sainz, R. et al.Advertised on:
102010 -
Scattering Polarization of Hydrogen Lines in Weakly Magnetized Stellar Atmospheres. I. Formulation and Application to Isothermal Models
Although the spectral lines of hydrogen contain valuable information on the physical properties of a variety of astrophysical plasmas, including the upper solar chromosphere, relatively little is known about their scattering polarization signals, whose modification via the Hanle effect may be exploited for magnetic field diagnostics. Here we report
Štěpán, J. et al.Advertised on:
52011 -
Scattering Polarization and Hanle Effect in Stellar Atmospheres with Horizontal Inhomogeneities
Scattering of light from an anisotropic source produces linear polarization in spectral lines and in the continuum. In the outer layers of a stellar atmosphere the anisotropy of the radiation field is typically dominated by the radiation escaping away, but local horizontal fluctuations of the physical conditions may also contribute, distorting the
Manso Sainz, R. et al.Advertised on:
122011 -
On the Sensitivity of Partial Redistribution Scattering Polarization Profiles to Various Atmospheric Parameters
This paper presents a detailed study of the scattering polarization profiles formed under partial frequency redistribution (PRD) in two thermal models of the solar atmosphere. Particular attention is given to understanding the influence of several atmospheric parameters on the emergent fractional linear polarization profiles. The shapes of these Q
Sampoorna, M. et al.Advertised on:
102010 -
On the Probable Existence of an Abrupt Magnetization in the Upper Chromosphere of the Quiet Sun
We report on a detailed radiative transfer modeling of the observed scattering polarization in the Hα line, which allows us to infer quantitative information on the magnetization of the quiet solar chromosphere. Our analysis suggests the presence of a magnetic complexity zone with a mean field strength langBrang > 30 G lying just below the sudden
Štěpán, J. et al.Advertised on:
32010
