case western reserve university



Model Atmospheres and Abundance Analyses of Main Sequence Stars

Ulrike Heiter (CWRU)

An important prerequisite for analysing the radiation emitted by the photospheres of stars is an assumption on the structure of these photospheres, i.e. a model of the change of thermodynamic quantities with depth. A summary of the methods employed in the ATLAS9 code (R. Kurucz) for calculating such model atmospheres, in particular concerning the convective energy transport, will be given. The calculation of large grids of model atmospheres enabled to quantify the effect of different convection treatments on model structure and observable quantities. The model atmospheres have also been used as outer boundary conditions for stellar interior models. The main steps involved in the determination of characteristic parameters and the chemical composition of stellar atmospheres ("abundance analysis") will be summarized. Results for a group of metal poor, population I, A-F type dwarfs, the lambda Bootis stars, and their significance for theories explaining the properties of this group will be given. As another application of abundance analysis, a project on high resolution spectroscopy of stars in the solar neighborhood will be outlined. Finally, the status of the metallicity distribution determined for dwarf stars accompanied by extrasolar giant planets will be reviewed and complemented by current results.