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The dynamical distance to M15: estimates of the cluster\u27s age and mass and of the absolute magnitude of its RR Lyrae stars

By B. J. McNamara, T. E. Harrison and H. Baumgardt


Newly determined high-precision relative proper motions determined from the Hubble Space Telescope Wide Field Planetary Camera 2 are used along with radial velocity measurements to determine the dynamical distance to the globular cluster M15. A comparison of the proper motion and radial velocity dispersions from a sample of 237 stars, located at an average radial distance of about 10" from the cluster center, yields a cluster distance of 9.98+/-0.47 kpc. This distance agrees to within the stated errors to other distance estimates but places this object about 5% closer than the currently adopted value of 10.4 kpc. Using this new distance, we estimate that RR Lyrae stars having [Fe/H]=-2.15 have a value of M-v(RR)=0.51+/-0.11. We also estimate that M 15 has an age of about 13.2 Gyr, which places it among the oldest of the Galactic globular clusters. From a comparison of the observed velocity dispersion with results from recent N-body calculations, we derive a total cluster mass for M 15 of M-C=4.5x10(5) M-circle dot

Topics: Distance scale, Globular clusters : individual (M15), Globular-Clusters, Astrometric Distances
Publisher: Institute of Physics Publishing
Year: 2004
DOI identifier: 10.1086/380905
OAI identifier:

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