On the Globular Cluster IMF Below 1 M_⊙

Abstract

Accurate luminosity functions (LF) for a dozen globular clusters have now been measured at or just beyond their half-light radius using HST. They span almost the entire cluster main sequence (MS) below ^ti 0.75 M_o. Transformation of the LF into mass functions (MF) by means of the available mass luminosity (ML) relations that are consistent with all presently available data on the physical properties of low mass, low metallicity stars shows that all the LF observed so far can be obtained from MF having the shape of a log-normal distribution with characteristic mass m, = 0.33 + 0.03 M_o and standard deviation a = 0.34 + 0.04. After correction for the effects of mass segregation, the variation of the ratio of the number of higher to lower mass stars with cluster mass or any simple orbital parameter or the expected time to disruption shows no statistically significant trend over a range of this last parameter of more than a factor of ^ti 100. We conclude that the global MF of these clusters have not been measurably modified by evaporation and tidal interactions with the Galaxy and, thus, should reflect the initial distribution of stellar masses.