Journal ArticleDOI
Modeling the scattering polarization of the solar Ca I 4227 Å line with angle-dependent partial frequency redistribution
Gioele Janett,Ernest Alsina Ballester,Ernest Alsina Ballester,Nuno Guerreiro,Simone Riva,L. Belluzzi,L. Belluzzi,Tanausú del Pino Alemán,Javier Trujillo Bueno,Javier Trujillo Bueno +9 more
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TLDR
In this article, the authors assess the impact and the range of validity of the angle-averaged (AA) approximation with respect to the general angle-dependent (AD) treatment of partial frequency redistribution (PRD) effects in the modeling of scattering polarization in strong resonance lines, with a focus on the solar Ca´I 4227 A line.Abstract:
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 applied.Aims. This work aims to assess the impact and the range of validity of the 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 a focus on the solar Ca I 4227 A line.Methods. Spectral line polarization was 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 was solved through a two-step approach. In step 1, the problem was solved for the intensity only, considering a multilevel atom. In step 2, the problem was 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 A 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 the 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 A 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.read more
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References
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Book
The observation and analysis of stellar photospheres
TL;DR: In this paper, the authors present a model of the photosphere of the black body and its radiation, and the measurement of stellar continua, spectral lines, and photospheric pressure.
Book
Iterative Solution of Large Sparse Systems of Equations
TL;DR: In the second edition of this classic monograph, complete with four new chapters and updated references, readers will now have access to content describing and analysing classical and modern methods with emphasis on the algebraic structure of linear iteration, which is usually ignored in other literature.
Journal ArticleDOI
Energy balance in the solar transition region. III - Helium emission in hydrostatic, constant-abundance models with diffusion
TL;DR: In this article, the authors discussed the limitations of the hydrostatic and one-dimensional assumptions used and analyzed the determination of helium emission when diffusion is included, using transport coefficients estimated from kinetic theory to determine the helium departures from local ionization balance.
Journal ArticleDOI
Multilevel Radiative Transfer with Partial Frequency Redistribution
TL;DR: In this article, a multilevel accelerated lambda iteration (MALI) method for radiative transfer calculations with partial frequency redistribution (PRD) is presented, which is based on Rybicki & Hummer's complete frequency redistribution formalism with full preconditioning, consistently accounts for overlapping radiative transitions.