LOW-LUMINOSITY STELLAR MASS FUNCTIONS IN GLOBULAR-CLUSTERS

New CCD photometry in selected fields in the globular clusters M13 and M71 is used to construct stellar luminosity and mass functions extending down the main sequence to at least 0.2 M⊙. The luminosity function of M71 is rather flat from M, = 3.5 through to M, = 7.5 and displays a sharp increase fainter than this to the limit of the data at M, = 10. The result for M13 is not significantly different from that obtained by Drukier et al., with the luminosity function being very steep at the faint end. Comparing the mass functions for M13 and M71 to existing data for NGC 6397, we find that all three display a marked change in slope at about 0.4 M⊙, with the slope becoming considerably steeper toward lower masses. The three systems span almost the full range of metallicity observed in the Galactic globular clusters, but no sign of a correlation between the slope of the mass function (at either high or low masses) and metallicity is seen. Both NGC 6397 and M71 appear to be in a more advanced stage of dynamical evolution than M13, and it is perhaps significant that the low-mass slope of the mass function is much steeper in M13. The implication of these results for the source of dark matter in the Galactic halo is discussed. © 1990. The American Astronomical Sodety. All rights reserved.