arXiv subjects

Tanausú del Pino Alemán

Publications and source records attributed to Tanausú del Pino Alemán.

23 records · Page 2Linked to original sources

arXiv2022

Formation of the Mg II h and k polarization profiles in a solar plage model and their suitability to infer magnetic fields

The Mg II h and k lines are among the strongest in the near-ultraviolet solar spectrum and their line core originates in the upper chromosphere, just below the transition region. Consequently, they have become one of the main targets for investigating the magnetism of the upper solar atmosphere. The recent CLASP2 mission obtained unprecedented spectropolarimetric data of these lines in an active region plage, which have already been used to infer the longitudinal component of the magnetic field by applying the weak field approximation. In this paper, we aim at improving our understanding of the diagnostic capabilities of these lines by studying the emergent Stokes profiles resulting from radiative transfer calculations in a radiative magneto-hydrodynamic (rMHD) time-dependent model representative of a solar plage. To this end, we create a synthetic observation with temporal and spatial resolutions similar to those of CLASP2. We find strong asymmetries in the circular polarization synthetic profiles which considerably complicate the application of the weak field approximation. We demonstrate that the selective application of the weak field approximation to fit different spectral regions in the profile allows to retrieve information about the longitudinal component of the magnetic field at different regions of the model atmosphere, even when the circular polarization profiles are not anti-symmetric and are formed in the presence of strong velocity and magnetic field gradients.

astro-ph.SR↗

arXiv2022

The circular polarization of the Mn I resonance lines around 280 nm for exploring chromospheric magnetism

We study the circular polarization of the Mn I resonance lines at 279.56, 279.91, and 280.19 nm (hereafter, UV multiplet) by means of radiative transfer modeling. In 2019, the CLASP2 mission obtained unprecedented spectropolarimetric data in a region of the solar ultraviolet including the Mg II h and k resonance lines and two lines of a subordinate triplet, as well as two Mn I resonance lines. The first analysis of such data, in particular those corresponding to a plage region, allowed the inference of the longitudinal magnetic field from the photosphere to the upper chromosphere just below the transition region. This was achieved by applying the weak field approximation to the circular polarization profiles of the Mg II and Mn I lines. While the applicability of this approximation to the Mg II lines was already demonstrated in previous works, this is not the case for the Mn I UV multiplet. These lines are observed as absorptions between the Mg II h and k lines, a region whose intensity is shaped by their partial frequency redistribution effects. Moreover, the only Mn I stable isotope has nuclear spin $I=5/2$ and thus hyperfine structure must be, a priori, taken into account. Here we study the generation and transfer of the intensity and circular polarization of the Mn I resonance lines accounting for these physical ingredients. We analyze their sensitivity to the magnetic field by means of their response function, and we demonstrate the applicability of the weak field approximation to determine the longitudinal component of the magnetic field.

astro-ph.SR↗

arXiv2021

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. Aims. This work aims at assessing the impact and the range of validity of the angle-averaged AA approximation with respect to the general angle-dependent (AD) treatment of PRD effects in the modeling of scattering polarization in strong resonance lines, with focus on the solar Ca i 4227 Å line. Methods. Spectral line polarization is modeled by solving the radiative transfer problem for polarized radiation, under nonlocal thermodynamic equilibrium conditions, taking PRD effects into account, in static one-dimensional semi-empirical atmospheric models presenting arbitrary magnetic fields. The problem is solved through a two-step approach. In step 1, the problem is solved for intensity only, considering a multi-level atom. In step 2, the problem is solved including polarization, considering a two-level atom with an unpolarized and infinitely sharp lower level, and fixing the lower level population calculated at step 1. Results. The results for the Ca i 4227 Å line show a good agreement between the AA and AD calculations for the Q/I and U/I wings signals. However, AA calculations reveal an artificial trough in the line-core peak of the linear polarization profiles, whereas AD calculations show a sharper peak in agreement with observations. Conclusions. An AD treatment of PRD effects is essential to correctly model the line-core peak of the scattering polarization signal of the Ca i 4227 Å line. By contrast, in the considered static case, the AA approximation seems to be suitable to model the wing scattering polarization lobes and their magnetic sensitivity through magneto-optical effects.

astro-ph.SR↗

arXiv2021

The polarization of the Lyman-$α$ 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 that emerge from given three-dimensional (3D) coronal models, and this should be done taking into account the symmetry breaking produced by the presence of magnetic fields and non-radial solar wind velocities. We have developed such a tool with the aim of theoretically predicting and interpreting spectropolarimetric observations of the solar corona in permitted and forbidden lines. In this paper we show the results of a theoretical investigation of the linear polarization signals produced by scattering processes in the H I Ly-$α$ line at 1216 A and in the He II Ly-$α$ line at 304 A using 3D coronal models by Predictive Science Inc. These spectral lines have very different critical magnetic fields for the onset of the Hanle effect (53 G and 850 G, respectively), as well as different sensitivities to the Doppler effect caused by the solar wind velocities. We study under which circumstances simultaneous observations of the scattering polarization in these Ly-$α$ lines can facilitate the determination of magnetic fields and macroscopic velocities in the solar corona.

astro-ph.SR↗

arXiv2016

Magnetic Diagnostics of the Solar Chromosphere with the Mg II h-k Lines

We investigated the formation of the Mg II h-k doublet in a weakly magnetized atmosphere (20-100 G) using a newly developed numerical code for polarized RT in a plane-parallel geometry, which implements a recent formulation of partially coherent scattering by polarized multi-term atoms in arbitrary magnetic field regimes. Our results confirm the importance of partial redistribution effects in the formation of the Mg II h and k lines, as pointed out by previous work in the non-magnetic case. We show that the presence of a magnetic field can produce measurable modifications of the broadband linear polarization even for relatively small field strengths (~10 G), while the circular polarization remains well represented by the classical magnetograph formula. Both these results open an important new window for the weak-field diagnostics of the upper solar atmosphere.

astro-ph.SR↗