Differents aspects de la modelisation des atmospheres stellaires des etoiles de types spectraux b a f
Institution:
Université Louis Pasteur (Strasbourg) (1971-2008)Disciplines:
Directors:
Abstract EN:
The first chapter was dedicated to test the ability of the current flux predictions in lte and re to reproduce the observed spectral energy distributions from the ultraviolet to the infrared range. Forty-one a and f stars were found to have appropriate spectrophotometry from the far uv to the ir. The infrared flux method was applied to derive their effective temperatures in a nearly fundamental manner. The most important disagreements between the observed seds and the theoretical seds were found to occur in the ultraviolet range. In a second chapter, the continuous opacity due to elements deemed to be important continuous opacity sources in the ultraviolet have been calculated using new data (topbase and iron project). The computed opacities have been compared with those currently used in atlas. The main differences in the flux distribution occur at wavelengths below 1600 a. The third chapter consists in a detailed study of the ultraviolet high resolution spectrum of the star hd72660 (a1v). For each studied line, a careful error analysis has been performed. The found abundances show that hd72660 is actually a hot am star. An ultraviolet spectral atlas of the star hd72660 has been constructed. The last part is dedicated to the search of vertical chemical stratification in the atmospheres of hgmn stars. Observations have been carried out on the blue and red sides of the balmer discontinuity in order to access lines formed at slightly different optical depths. Contribution functions were computed in order to derive the depth of formation of the flux across each line. For the spectroscopic binary hgmn star hd143807, iron (fe) may be vertically stratified.
Abstract FR:
Une premiere partie a consiste a tester la capacite des modeles a reproduire les distributions d'energie spectrale observees du domaine ultraviolet au domaine infrarouge. La temperature effective necessaire a une telle comparaison a ete determinee par la methode des flux infrarouges. 41 etoiles naines ou sous-geantes de types spectraux a et f ont ete etudiees. Les desaccords les plus importants entre les distributions d'energie spectrale theoriques et les distributions d'energie spectrale observees sont constates dans le domaine ultraviolet. Dans une deuxieme partie, l'opacite continue de certains elements a ete calculee en integrant de nouvelles donnees (topbase et iron project). Les valeurs obtenues ont ete comparees avec celles utilisees jusqu'a present. Pour les etoiles de type spectral a, les principaux desaccords sont constates pour des longueurs d'onde inferieures a 1600 a. Une troisieme partie a consiste en une etude dans le domaine ultraviolet de l'etoile hd72660 (a1v). Pour chaque raie etudiee, l'incertitude sur l'abondance a ete determinee de faÇon detaillee. Les resultats obtenus pour les abondances confirment le caractere am de l'etoile hd72660. Un atlas de spectres ultraviolets de l'etoile hd72660 a ete construit. Dans une derniere partie, afin de mettre en evidence l'existence d'atmospheres stellaires stratifiees dans les etoiles hgmn, des observations ont ete effectuees de chaque cote de la discontinuite de balmer. Les fonctions de contribution des differentes raies ont permis de determiner la profondeur d'ou le flux formant la raie est issu. Pour l'etoile hgmn hd143807, seul le fer (fe) semble presenter une repartition non-homogene de son abondance.