Initial mass function in the South-Western part of M 31

Abstract

We derive an average initial mass function (IMF) for 50 OB associations in the South-Western part of Andromeda galaxy, combining ultraviolet photometry of Hill et al. (1995, ApJ, 98, 595) and two datasets HST photometry with JHK s photometry from the 2MASS + I band photometry from Magnier et al. (1992, A&A, 96, 379). The mean extinctions within the associations were estimated in two independent ways and the stellar masses were determined by use of probabilistic techniques. The derived slope of the IMF Γ = -1.59 ± 0.09 is close to the universal Salpeter's law and to recent estimates for massive stars' IMF in the Galaxy and in the Magellanic Clouds.