Modélisation du spectre de l'hélium dans les protubérances solaires

Abstract : This thesis deals with the modelling of the helium spectrum in solar quiescent prominences. Prominences are magnetic structures confining a cold, dense plasma in the hot, tenuous surrounding solar corona. Despite its great importance, no theoretical calculations on a large range of the observed helium spectrum in quiescent prominences have been performed out of Local Thermodynamic Equilibrium (LTE) since previous work by Heasley and co-workers (published between 1974 and 1983). This study aims at carrying out new non LTE computations, removing several restrictions that were present in the work of Heasley et al. We get the helium emergent spectrum of a one-dimensional, isothermal and isobaric prominence, considering 34 energy levels in our multi-ion helium model (He I + He II + He III). The present theoretical study shows the different effects of the physical parameters of our models on the main helium level populations, as well as on the emitted intensities. Part of this work has also been devoted to the comparisons with observations taken by the SUMER and CDS spectrometers onboard SoHO, thus leading to a diagnostic of the observed structure. This study deals only with quiescent solar prominences, for isothermal and isobaric models. The non LTE diagnostic tool which is now available brings a considerable improvement for the interpretation of observations. Some perspectives would be to have a better understanding of the helium spectrum formation under different physical conditions, and to apply our diagnostic method to other solar atmosphere structures and to other astrophysical situations.
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Submitted on : Tuesday, October 28, 2003 - 12:23:57 PM
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Nicolas Labrosse. Modélisation du spectre de l'hélium dans les protubérances solaires. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00003651⟩

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