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Kinetic theory methods applied to stellar atmosphere spectroscopy

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Thesis advisor : Joël Rosato
Email and address : joel.rosato
Tel : +33-491288624

Subject description :
Spectroscopic models are routinely used in astrophysics for diagnostic purposes, given the dependence of spectra on the physical parameters (density, temperature of ions and electrons, etc.) that characterize plasmas. The aim of this project is to investigate the broadening of atomic lines due to the emitters’ thermal motion (Doppler broadening) and the microscopic electric field (Stark broadening) in conditions relevant to stellar atmospheres, in order to improve the accuracy of diagnostics. The student will have to design models applicable to out-of-equilibrium plasmas. A special emphasis will be devoted to approaches that employ kinetic theory. Recent works carried out in the framework of magnetic fusion research have reported on improvements of diagnostic routines done with such approaches (modeling of non Maxwellian distributions and mesoscopic scale fluctuations [1] ; collision operators accounting for nonbinary interactions [2]), with a potential application to the lines observed in tokamak edge and divertor plasmas. This is of particular use for stellar atmosphere plasmas due to their similar conditions, in particular in stars of A and DA type given the strong hydrogen lines they present. After investigating the theoretical methods, the student will have to perform spectra calculations in realistic conditions. Comparisons to experimental spectra will be made. Radiative transfer, a major issue in stellar atmosphere spectroscopy, will also be investigated. In this framework, new analyses using a reformulation of the theory based on quantum electrodynamics [3] will be performed.
Bibliography :
[1] R. Stamm et al., Eur. Phys. J. D, submitted.
[2] J. Rosato, H. Capes, and R. Stamm, Phys. Rev. E 86, 046407 (2012).
[3] J. Rosato, Phys. Rev. Lett. 107, 205001 (2011).