1994A&A...287..885H

We have observed a number of the most luminous A and B supergiants in the galaxies M 31 and M 33 at intermediate dispersion obtaining both blue and red spectrograms. We have determined spectral types and luminosity classifications from these data, in a few cases revising previous evaluations. From comparison with galactic analogues we estimate approximate metallicities for M 31 and M 33. In addition, for the first time we present H_α profiles for these stars which we use to estimate mass loss rates. We conclude that M 31 is comparable in metallicity to our galaxy but M 33 is slightly deficient, more precise estimates requiring higher resolution data. The H_α data are morphologically similar to those of galactic stars and clearly contradict claims that mass-loss rates for luminous stars in M 31 are up to a factor of ten less than their galactic counterparts. We note in particular that the M 31 star 40-1939 is confirmed here as a B1Ia⁺ hypergiant rather than an O6I supergiant (Hutchings et al. 1987) thus explaining the absence of typical wind features associated with an O6 classification. Also of particular interest are the luminous A-hypergiants in M 33, B324 especially appears to be more luminous than any comparable star in our galaxy or the Magellanic Clouds, has an H_α equivalent width of 40A in emission and exhibits a number of FeII P-Cygni profiles.