Multidimensional non-LTE radiative transfer. Application to the helium spectrum in solar prominences.

Radiative transfer is an essential theory in astrophysics. Developing new realistic numerical tools, faster and more precise, is still relevant to improve data exploitation of numerous existing and future instruments. The first part of my work was to develop a new non Local Thermodynamical Equilibrium (non-LTE) radiative transfer code in 2D cartesian geometry for multilevel atoms. This code is based on Gauss-Seidel/Successive Over-Relaxation (SOR) algorithms combined with multigrid techniques (Paletou & Léger 2007, Léger et al. 2007). The second part was to apply this code to the study of the He I spectrum in solar prominences. Some of its multiplets are often used to diagnose the magnetic field in those structures. The atomic fine structure of He I is taken into account, which allows to synthesize spectral lines directly comparable with high spectral resolution observations made at THéMIS for example. Geometrical effects are highlighted in the formation of those multiplets. Finally first computations of He I spectrum considering filamentary structures in 2D geometry have been made (Léger & Paletou 2008).