ar X iv : a st ro - p h / 96 12 11 6 v 1 1 1 D ec 1 99 6 Fabry - Perot Observations of Globular Clusters III : M 15

We have used an Imaging Fabry-Perot Spectrophotometer with the Sub-arcsecond Imaging Spectrograph on the Canada-France-Hawaii Telescope to measure velocities for 1534 stars in the globular cluster M15 (NGC 7078) with uncertainties between 0.5 and 10 km s. Combined with previous velocity samples, the total number of stars with measured velocities in M15 is 1597. An average seeing of 0.8 allowed us to obtain velocities for 144 stars within 10 of the center of M15, including 12 stars within 2. The velocity dispersion profile for M15 remains flat at a value of 11 km s from a radius of 0.4 into our innermost reliable point at 0.02 (0.06 pc). Assuming an isotropic velocity dispersion tensor, this profile and the previouslypublished surface brightness profile can be equally well represented either by a stellar population whose M/L varies with radius from 1.7 in solar units at large radii to 3 in the central region, or by a population with a constant M/L of 1.7 and a central black hole of 1000 M⊙. A non-parametric mass model that assumes no black hole, no rotation, and isotropy constrains the mass density of M15 to better than 30% at a radius of 0.07 parsecs. The mass-density profile Visiting Astronomer, Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.