Globular Cluster Photometry With The Hubble Space Telescope. II. U,V, And I Measurements of M15
Abstract
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 ralpha, with alpha approximately -0.85 +/- 0.2, or with a King model with a core of radius approximately less than 2 sec. 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 103 stars (and in U, V, and I of approximately greater than 1500 stars) are used to construct color-magnitude diagrams in the central 1 min of M15. Fourteen blue straggler candidates are identified in the inner 20 sec. 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.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 1994
- DOI:
- 10.1086/116983
- Bibcode:
- 1994AJ....107.1745Y
- Keywords:
-
- Astronomical Photometry;
- Blue Stars;
- Density Distribution;
- Globular Clusters;
- Hubble Space Telescope;
- M Stars;
- Cameras;
- Charge Coupled Devices;
- Computerized Simulation;
- High Resolution;
- Monte Carlo Method;
- Optical Filters;
- Spatial Resolution;
- Astronomy;
- GALAXIES: INDIVIDUAL: M15;
- GLOBULAR CLUSTERS: GENERAL;
- GALAXIES: NUCLEI