RADIATION-DRIVEN WINDS OF HOT STARS - THEORY OF O-STAR ATMOSPHERES ASA SPECTROSCOPIC TOOL

The status of the continuing effort to construct radiation driven wind models for O-Stars atmospheres is reviewed. Emphasis is given to seve ral problems relating to the fomation of UV line spectra the use of ac curate atomic data, the inclusion of EUV radiation by shock heated mat ter, the simulation of photospheric line blocking. A new tool for O-st ar diagnostics is presented. This is based on the use of wind models t o calculate synthetic high resolution spectra covering the observable UV region. A comparison with observed spectra then gives physical cons traints on the properties of stellar winds and stellar parameters, add itionally abundances can be determined. The astrophysical potential of this method is demonstrated by an application to two Of-stars, the ga lactic O4f-star zeta-Puppis and the LMC O3f-star Melnick 42. With rega rd to effective temperatures and gravities, the results from the appli cation of classical methods to the analysis of photospheric lines are only partially verified. Explanations for the shortcomings of classica l NLTE methods are discussed.