GLOBULAR-CLUSTER PHOTOMETRY WITH THE HUBBLE-SPACE-TELESCOPE .2. U, V, AND I MEASUREMENTS OF M15

The projected density distribution of resolved stars near the center of M15 is shown to be consistent with either a power-law cusp N(r) approximately r(alpha) with alpha approximately -0.85 +/- 0.2, or with a King model with a core of radius less-than-or-equal-to 2'' (best fit r(core) = 1.3''). The inferred slope is in agreement with the theoretical value, alpha = -0.75, calculated by Bahcall and Wolf for the distribution of equal-mass stars surrounding a massive black hole and is also consistent with the radial profile expected from core collapse without a central black hole. The object AC 214 is a candidate for the central density cusp. Analysis of Monte Carlo simulations of the diffuse light indicates that, using current analysis techniques and available data, the residual light is not a reliable indicator of the true density distribution. This is contrary to earlier work. Photometric measurements in V and I of more than 5 x 10(3) stars (and in U, V, and I of greater-than-or-similar-to 1500 stars) are used to construct color-magnitude diagrams in the central 1' of M15. Fourteen blue straggler candidates are identified in the inner 20''. The central color gradient noticed by previous researchers is caused by a central depletion of bright red giant stars rather than an excess of blue stragglers or blue horizontal branch stars.