THE STELLAR WIND OF AN O8.5I(F) STAR IN M31 - A DETERMINATION OF MASS-LOSS RATE AND METALLICITY

We rediscuss the UV spectrum of OB 78#231, an O8.5 I(f) star in the An dromeda galaxy M 31, which has been obtained with the Faint Object Spe ctrograph on the Hubble Space Telescope by Hutchings et al. (1992). Th e spectrum has been reextracted with better knowledge of background, c alibration, and scattered light. The empirical analysis of the stellar wind lines results in a terminal velocity and mass loss rate similar to those typically found in comparable galactic objects. Furthermore, a comparison with an FOS spectrum of an O7 supergiant in the Small Mag ellanic Cloud and IUE spectra of galactic objects implies a metallicit y close to galactic counterparts. These results are confirmed quantita tively by spectrum synthesis calculations using a theoretical descript ion of O-star winds.