Mass loss rates from O stars in OB associations.

Abstract

The considered investigation is concerned with an extension of an analysis of the spectra of 31 O type stars observed with the International Ultraviolet Explorer (IUE) satellite to include excited as well as resonant lines. The investigation makes use of the methods developed by Olson (1981). Most of the stars are unevolved cluster members, a group which has not been treated in previous studies. Attention is given to the theory and techniques for mass loss rate determination, the correlation of mass loss with various stellar parameters, and a comparison of the obtained results with the predictions of models. A major consequence of the derived mass loss relationship is that mass loss by stellar winds will affect the evolution of only very luminous (massive) stars. It is, however, emphasized that the obtained relationship is dominated by main-sequence O stars. It is found that the subordinate lines of N IV and O IV are much weaker than what is expected in O stars.