The Helium spectrum in erupting solar prominences

Even quiescent solar prominences may become active and sometimes erupt. These events are occasionally linked to coronal mass ejections. However we know very little about the plasma properties during the activation and eruption processes. We present new computations of the helium line profiles emitted by an eruptive prominence. The prominence is modelled as a plane-parallel slab standing vertically above the solar surface and moving upward as a solid body. The helium spectrum is computed with a non local thermodynamic equilibrium radiative transfer code. The effect of Doppler dimming / brightening is investigated in the resonance lines of He I and He II formed in the EUV, as well as on the He I 10830 A and 5876 A lines. We focus on the line profile properties and the resulting integrated intensities. It is shown that the helium lines are very sensitive to Doppler dimming effects. We also study the effect of frequency redistribution in the formation mechanisms of the resonance lines and find that it is necessary to use partial redistribution in frequency for the resonance lines.Comment: 5 pages, 4 figures. Proceedings of IAU GA 2006, JD03: Solar Active Regions and 3D Magnetic Structure. See also a more detailed paper at astro-ph/060822

Spectral Diagnostics of Active Prominences

Active prominences exhibit plasma motions, resulting in difficulties with the interpretation of spectroscopic observations. These solar features being strongly influenced by the radiation coming from the solar disk, Doppler dimming or brightening effects may arise, depending on which lines are observed and on the velocity of the plasma. Interlocking between the different atomic energy levels and non local thermodynamic equilibrium lead to non-trivial spectral line profiles, and this calls for complex numerical modelling of the radiative transfer in order to understand the observations. We present such a tool, which solves the radiative transfer and statistical equilibrium for H, He I, He II, and Ca II, in moving prominences where radial plasma motions are taking place. It is found that for isothermal, isobaric prominence models, the He II resonance lines are very sensitive to the Doppler effect and show a strong Doppler dimming. The Ca II lines are not very sensitive to the Doppler effect for the prominence models considered here. We illustrate how the code makes it possible to retrieve the plasma thermodynamic parameters by comparing computed and observed line profiles of hydrogen and helium resonance lines in a quiescent prominence.Comment: 6 pages, 5 figures. In press,"Physics of Chromospheric Plasmas" (Coimbra), ASP 368, 337 (2007). Revised version matches published version

Formation of helium lines in solar prominences

We summarize the results on the formation of the helium spectrum in solar prominences obtained over recent years. The radiative transfer problem under non-LTE conditions is solved to compute the profiles of the lines of He I and He II. The structure of the prominence-to-corona transition region (PCTR) has a major influence on the resulting spectrum of the resonance lines since they are formed mostly in this part of the prominence. However, subordinate lines are also affected by the structure of the PCTR. We pay particular attention to the formation of the He II 304 Å resonance line which is routinely observed from space, but yet not fully understood. Future steps in the modelling will be addressed

Modélisation du spectre de l'hélium dans les protubérances solaires

Cette thèse porte sur la modélisation du spectre de l'hélium dans les protubérances solaires quiescentes. Les protubérances sont des stuctures magnétiques confinant un plasma froid et dense par rapport au plasma coronal environnant. Malgré sa très grande importance, aucun calcul théorique hors Equilibre Thermodynamique Local (ETL) n'a été mené sur une large gamme du spectre de l'hélium observable dans les protubérances depuis les travaux de Heasley et ses collègues, parus entre 1974 et 1983. Cette étude s'attache donc à effectuer de nouveaux calculs hors ETL, en éliminant de nombreuses restrictions présentes dans les travaux de Heasley et al. On obtient le spectre émergent de l'hélium dans une protubérance à une dimension, isotherme et isobare, pour un modèle d'hélium à 34 niveaux d'énergie (He I + He II + He III).Les études théoriques menées ici montrent les différents effets que peuvent avoir les paramètres physiques de nos modèles sur les populations des principaux niveaux d'énergie de l'hélium ainsi que sur les intensités émises...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...ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Formation des raies spectrales et oscillations dans la chromosphere solaire

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Voyage, quête, pèlerinage dans la littérature et la civilisation médiévales

Voici les actes du colloque organisé par le C.U.E.R. M.A les 5, 6, 7 Mars 1976 sur le thème VOYAGE, QUETE, PELERINAGE DANS LA LITTERATURE ET LA CIVILISATION MEDIEVALES. Le tirage offset a été réalisé à partir des dactylogrammes fournis par chacun des auteurs de communications. Ce procédé entraîne malheureusement, outre des imperfections de détail, une disparité de caractères typographiques d'un article à l'autre. Cette solution a pourtant été retenue car elle permettait d'obtenir une publication rapide à un coût non prohibitif. Les communications du colloque ont été regroupées par centre d'intérêt ainsi qu'il apparaît clairement dans la table des matières. Deux études, celles de Madame ROSSI et de Monsieur TAVERA, qui, pour des questions d'horaires, n'avaient pu être présentées, sont insérées au volume. L'Université de Provence et l'U.E.R. Arts-Lettres—Expression ont bien voulu subventionner le colloque et participer à son organisation et à l'impression de ses travaux. La librairie Honoré CHAMPION a accepté d'en assurer la diffusion. Le bureau et le conseil d'administration du C.U.E.R. M.A. se font un agréable devoir de les en remercier