UV and optical spectroscopy of OB stars in M 31 and M 33.
Bianchi, L.; Hutchings, J. B.; Massey, P.
United States, Canada, Italy
Abstract
IUE UV spectra and MMT blue spectra have been obtained for 'normal' OB supergiant stars in M31 and M33. The authors classify the stars as late O to early B. UV and visible fluxes yield consistent values for the effective temperature, bolometric magnitudes, and extinction for the stars. The UV resonance lines have very low outflow velocities compared with galactic stars, and no P Cygni profiles. The UV interstellar extinction in both galaxies appears to be like the LMC and not like the galaxy. These and other initial results on stellar winds in M31 and M33 are discussed, and suggest that there may be significant differences in mass-loss mechanisms among Local Group galaxies.