The winds of hot stars in M31 and M33
Optical ground based (MMT, KFHT, KPNO) and UV IUE observations of bright blue stars in M31 and M33 have been collected over the past years. The spectral types, Teff and bolometric luminosities are derived from UV and visible spectra, and CCD optical photometry. The stars are all of 0, B and WR type of high luminosity. Compared with galactic stars of similar types, the UV line spectrum and in particular the stellar wind indicators are weak, and the terminal velocities are low, in both galaxies. Early results were published in Massey et al. (1985) and in Hutchings et al (1987), and nine more stars are discussed, together with the previous data, in Bianchi et al (1991). The similarity of the wind features to MC's rather than to galactic counterparts, is hard to explain in M31, supposed to have a higher metallicity than Milky Way. The only possible explanation could be that we have so far studied the brightest stars, all in OB associations, that might be peculiar, or-else that a large metallicity gradient is present with radial distance in the galaxy. Both these hypoteses will be hopefully clarified by forthcoming HST observations.