AAS 199th meeting, Washington, DC, January 2002
Session 91. Stellar Populations and Galactic Structure
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall

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[91.13] Proper Motion Dispersions in Two Bulge Fields using HST/WFPC2

K. Kuijken (University of Groningen), R.M. Rich (UCLA)

We have measured very precise relative proper motions for thousands of stars in two fields in the Galactic Bulge, obtained from two epochs of HST/WFPC2 imaging separated by 6 years. We report relative proper motions and B,V photometry for the fields Sgr I (l,b)=(0.9,-2\circ) and Baade's Window (l,b)=(1,-4\circ). For the first time, we can easily separate the disk main sequence from the old bulge population by applying proper motion criteria alone. Based on this we are able to put very strong limits on any possible population of blue stragglers in the bulge, because no stars brighter than the old main sequence turnoff are found to have proper motions consistent with those of the bulge population. Our proper motion dispersions are \sigma(l)=0.29\prime\prime cent-1 and \sigma(b)=0.26\prime\prime cent-1 in Baade's Window. We find \sigma(l)=0.32 and \sigma(b)=0.28\prime\prime cent-1 in Sgr I; errors in these dispersions are smaller than 0.01\prime\prime cent-1 and are more determined by the population cut than by statistics or systematics. The Baade's Window dispersions are in good agreement with other studies, and the decline in velocity dispersion with increasing Galactic latitude is in agreement with self-consistent bulge models.

R.M. Rich acknowledges support from Grant GO-8250 through the Space Telescope Science Institute.

The author(s) of this abstract have provided an email address for comments about the abstract: rmr@astro.ucla.edu

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