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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

Abstract

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
OAI identifier: oai:espace.library.uq.edu.au:UQ:265881

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