Fast 2D non–LTE radiative modelling of prominences

Léger, L.; Chevallier, L.; Paletou, F.

doi:10.1051/0004-6361:20066730

Cited by 16 publications

(15 citation statements)

References 22 publications

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“…Multi-level and multi-dimensional cases will be considered further. However, the use of BiCG-P does not require the cumbersome modifications of multi-dimensional formal solvers required by GS/SOR methods (see e.g., Léger et al 2007).…”

Section: Discussionmentioning

confidence: 99%

A conjugate gradient method for solving the non-LTE line radiation transfer problem

Paletou¹,

Anterrieu²

2009

A&A

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This study concerns the fast and accurate solution of the line radiation transfer problem, under non-LTE conditions. We propose and evaluate an alternative iterative scheme to the classical ALI-Jacobi method, and to the more recently proposed Gauss-Seidel and successive over-relaxation (GS/SOR) schemes. Our study is indeed based on applying a preconditioned bi-conjugate gradient method (BiCG-P). Standard tests, in 1D plane parallel geometry and in the frame of the two-level atom model with monochromatic scattering are discussed. Rates of convergence between the previously mentioned iterative schemes are compared, as are their respective timing properties. The smoothing capability of the BiCG-P method is also demonstrated.

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Section: Discussionmentioning

confidence: 99%

A conjugate gradient method for solving the non-LTE line radiation transfer problem

Paletou¹,

Anterrieu²

2009

A&A

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“…More efficient iteration methods based on the Gauss-Seidel scheme have been developed for complete frequency redistribution (see e.g. Trujillo Bueno & Fabiani Bendicho 1995;Léger et al 2007). …”

Section: A Pali Type Numerical Methods Of Solutionmentioning

confidence: 99%

The Hanle effect in a random magnetic field

Frisch

Anusha²,

Sampoorna³

et al. 2009

A&A

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Context. The Hanle effect is used to determine weak turbulent magnetic fields in the solar atmosphere, usually assuming that the angular distribution is isotropic, the magnetic field strength constant, and that micro-turbulence holds, i.e. that the magnetic field correlation length is much less than a photon mean free path. Aims. To examine the sensitivity of turbulent magnetic field measurements to these assumptions, we study the dependence of Hanle effect on the magnetic field correlation length, its angular, and strength distributions. Methods. We introduce a fairly general random magnetic field model characterized by a correlation length and a magnetic field vector distribution. Micro-turbulence is recovered when the correlation length goes to zero and macro-turbulence when it goes to infinity. Radiative transfer equations are established for the calculation of the mean Stokes parameters and they are solved numerically by a polarized approximate lambda iteration method. Results. We show that optically thin spectral lines and optically very thick ones are insensitive to the correlation length of the magnetic field, while spectral lines with intermediate optical depths (around 10-100) show some sensitivity to this parameter. The result is interpreted in terms of the mean number of scattering events needed to create the surface polarization. It is shown that the single-scattering approximation holds good for thin and thick lines but may fail for lines with intermediate thickness. The dependence of the polarization on the magnetic field vector probability density function (PDF) is examined in the micro-turbulent limit. A few PDFs with different angular and strength distributions, but equal mean value of the magnetic field, are considered. It is found that the polarization is in general quite sensitive to the shape of the magnetic field strength PDF and somewhat to the angular distribution. Conclusions. The mean field derived from Hanle effect analysis of polarimetric data strongly depends on the choice of the field strength distribution used in the analysis. It is shown that micro-turbulence is in general a safe approximation.

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“…-We solve the statistical equilibrium equations (SEE) including ionization balance, and the non-LTE radiative transfer equations self-consistently, for the multilevel hydrogen atom, using the previously mentioned 2D radiative transfer code Léger et al 2007). We thus obtain bound-level populations and electron densities (see also Paletou 1995;Heinzel 1995, for the treatment of the ionization equilibrium), which defines the physical conditions to be used as input to the computation of the helium atom.…”

Section: Numerical Strategymentioning

confidence: 99%

“…To this end, we applied our own 2D radiative transfer code Léger et al 2007), which is based on the multigrid GaussSeidel/SOR iterative schemes proposed by Trujillo Bueno & Fabiani Bendicho (1995) and Fabiani Bendicho et al (1997) for radiative transfer applications.…”

Section: Introductionmentioning

confidence: 99%

2D non-LTE radiative modelling of He I spectral lines formed in solar prominences

Léger

Paletou

2009

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Context. The interpretation of high-resolution spectropolarimetric observations of solar prominences completed primarily at visible and near-infrared wavelengths, requires radiative modelling that takes into account both multi-dimensional geometry and complex atomic models.Aims. We enhance the interpretation of observations of He i multiplets, by considering 2D non-LTE unpolarized radiation transfer, and taking into account of the atomic fine-structure of helium. Methods. We apply our 2D non-LTE radiative transfer code, which is based on the multi-grid Gauss-Seidel/SOR iterative schemes.Results. It allows us to compute realistic emergent intensity profiles for the He i λ10 830 Å and D 3 multiplets, which can be directly compared to the simultaneous and high-resolution observations completed at THéMIS. A preliminary 2D multi-thread modelling is also discussed.

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Fast 2D non–LTE radiative modelling of prominences

Cited by 16 publications

References 22 publications

A conjugate gradient method for solving the non-LTE line radiation transfer problem

A conjugate gradient method for solving the non-LTE line radiation transfer problem

The Hanle effect in a random magnetic field

2D non-LTE radiative modelling of He I spectral lines formed in solar prominences

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