MASS-TO-LIGHT RATIOS FOR GLOBULAR-CLUSTERS .2. THE LOW-CONCENTRATION CLUSTERS NGC-288, NGC-54668 AND M55 (NGC-6809)

We have measured radial velocities, accurate to approximately 1 km s-1, for 20-30 stars in each of the three low-concentration globular clusters NGC 288, NGC 5466, and M55. These data are sufficient to calculate velocity dispersions and M/L's for these clusters, which we use to investigate their stellar populations. We have fit single- and multicomponent King models to our velocity data and to surface-brightness profiles taken from the literature. NGC 288 has a projected central M/L, (M/L(v))0, of 2.1 +/- 0.5 (in units of M./L(v).), NGC 5466 has (M/L(v))0 = 1.0 +/- 0.4, and M55 has (M/L(v)0 = 1.3 +/- 0.4. Our results are: (1) The (M/L)0's of NGC 288, NGC 5466, and M55 do not differ significantly from each other or from those of the cluster population as a whole. (2) The (M/L)0 of NGC 288 is lower than would be expected for a cluster that had a power law initial mass function as shallow as the observed present-day main-sequence mass function. (3) Models with initial mass functions consisting of two power law segments fit NGC 288 best when 50%-70% of the cluster mass is in stellar remnants, which would imply that 1.0-2.0 times the present cluster mass was lost due to stellar evolution alone in forming these remnants. (4) Because of the small amount of mass segregation expected in low-concentration clusters, we are able to place the first strong limits on the number of low-mass stars in a globular cluster, and thus on the total cluster masses and global M/L's. Fitting King models with different lower cutoffs for the power law mass functions produces a 97.5% confidence upper limit on the global M/L(v) of 2.5 for NGC 5466 and 3.4 for M55. The corresponding lower limits to the mass-function cutoff are approximately 0.2 M. and approximately 0.1 M., respectively, with the best match to the dynamical M/L occurring for a cutoff above approximately 0.4 M. and at approximately 0.3 M., respectively.