The Local Stellar Initial Mass Function

TL;DR

This paper discusses the challenges in determining the local stellar initial mass function (IMF) from star-count data, highlighting the importance of various factors and the potential of upcoming space missions to improve understanding.

Contribution

It reviews the methods and uncertainties in inferring the local IMF and emphasizes the role of future astrometry missions in advancing the field.

Findings

The local IMF can be approximated by a two-part power-law.

The IMF slope is alpha=1-1.5 for stars below 0.5 Msun.

The IMF slope is alpha=2.3 (Salpeter) for more massive stars.

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.