The stellar wind of an O8.5I(f) star in M31. A determination of mass loss rate and metallicity.
Lennon, D. J.; Bianchi, L.; Pauldrach, A. W. A.; Puls, J.; Haser, S. M.; Hutchings, J. B.; Kudritzki, R. -P.
Germany, Canada
Abstract
We rediscuss the UV spectrum of OB78#231, an O8.5I(f) star in the Andromeda galaxy M31, which has been obtained with the Faint Object Spectrograph on the Hubble Space Telescope by Hutchings et al.. The spectrum has been reextracted with better knowledge of background, calibration, 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 Magellanic Cloud and IUE spectra of galactic objects implies a metallicity close to galactic counterparts. These results are confirmed quantitatively by spectrum synthesis calculations using a theoretical description of O-star winds.