AAS 205th Meeting, 9-13 January 2005
Session 85 Star Clusters and Associations
Oral, Tuesday, January 11, 2005, 2:00-3:30pm, Royal Palm 1-3

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[85.06] IRS 16SW - A New Cluster of Young Stars in the Central Parsec of Our Galaxy.

J. R. Lu, A. M. Ghez, S. D. Hornstein, M. Morris, E. E. Becklin (UCLA)

One of the most perplexing problems associated with the supermassive black hole at the center of our Galaxy is the origin of the young stars in its close vicinity. In order to investigate this problem, we present new proper motion measurements based on 9 years of diffraction-limited K(2.2 \mum)-band adaptive optics and speckle imaging at the W. M. Keck 10 meter telescopes. Proper motions, along with stellar number density counts, reveal a new comoving group of stars, which we call the IRS 16SW cluster, located 3'' from the central black hole. Two of the six members of this comoving group (IRS 16SW and 16SW-E) are known He I emission line stars and have been identified as massive young stars in the Wolf-Rayet phase of post main sequence evolution. Based on their dynamical association, the remaining four stars are newly identified as young stars. Outside of the central stellar cusp, this is the second cluster within the central parsec of the Milky Way to be recognized. Possible origins include the surviving cores of massive infalling clusters or fragmentation and collapse of either colliding gas clouds or a massive pre-existing accretion disk. The dynamical coherence of this moving group of stars constrains its line-of-sight distance to the central black hole, the total cluster mass, and the age of the cluster.

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