The Local Stellar Initial Mass Function

Abstract

This contribution describes the difficult task of inferring the IMF from local star-count data, by discussing the mass-luminosity relation, unresolved binary, triple and quadruple systems, abundance and age spreads and Galactic structure, all of which must be accounted for properly for the results to be meaningful. A consensus emerges that the local IMF may be represented by a two-part power-law, with indices alpha=1-1.5 for stars with mass m<0.5 Msun, and the Salpeter value alpha=2.3 for more massive stars, but some uncertainties remain. Notable is also that the sensitivity of the stellar luminosity function (LF) to the derivative of the mass-luminosity relation is very evident in the (local) Hipparcos and HST, open-cluster and globular-cluster LFs, thus allowing tests of stellar structure theory. The upcoming astrometry space missions DIVA and GAIA will undoubtedly lead to significant advances in this field.