AAS 207th Meeting, 8-12 January 2006
Session 98 Seeing the Universe in a New (Sodium) Light: Early Science Results from Laser Guide Star Adaptive Optics
Special Session, Tuesday, 2:00-3:30pm, January 10, 2006, Delaware A

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[98.06] Constraints on Orbits and Origins of Young Stars in the Central Parsec of the Galaxy

J. R. Lu, A. M. Ghez (UCLA), K. Y. Matthews (Caltech), S. D. Hornstein, M. Morris, M. Rafelski, E. E. Becklin (UCLA), D. J. Thompson (Caltech), D. Le Mignant, P. Wizinowich, R. D. Campbell, J. C. Y. Chin, M. A. van Dam, S. K. Hartman, E. M. Johansson, R. E. Lafon, P. J. Stomski, D. M. Summers, A. Bouchez (Keck Observatory)

We present new proper motions for the apparently massive, young stars at the Galactic Center, based on observations obtained with the Keck laser guide star-adaptive optics (LGS-AO) system. Our proper motion measurements now have uncertainties of only 1-2 km/s, thanks to the LGS-AO observations that have allowed us to retroactively increase the accuracy, by a factor of ~10, and precision of over 10 years of speckle astrometry. With new proper motions, we explore the origin of these young stars, which is challenging given that the strong tidal forces of the supermassive black hole should suppress star formation. Their presence, however, may be explained either by star formation in an accretion disk or as the remnants of a massive stellar cluster which spiraled in via dynamical friction. Earlier stellar velocity vectors were used to postulate that all the young stars resided in two counter-rotating stellar disks, which would be consistent with both of the above formation scenarios. Our precise proper motions allow us, for the first time, to constrain the true orbit of each individual star and test the hypothesis that the massive stars reside in two counter-rotating stellar disks. We find that all 9 of the young stars in this study previously proposed to lie on the inner disk exhibit orbital constraints consistent with such a disk. On the other hand, of the 3 stars in this study previously proposed to lie in the outer disk, 2 exhibit inclinations that are inconsistent with such a disk, bringing into question the exsitance of the outer disk. Additionally, most stars in the inner disk have eccentric orbits. Although infalling cluster formation scenarios allow for eccentric orbits, accretion disk formation scenarios typically imply circular orbits, which is not supported by the observations.

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