A Large Proper-Motion Survey in Plaut's Low-Extinction Window

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We present preliminary results from the deepest and largest photographic proper-motion survey ever undertaken of the Galactic bulge. Our first-epoch plate material (from 1972-3) goes deep enough (Vₗim = 22) to reach below the bulge main-sequence turnoff. These plates cover an area of approximately 25 arc-min X 25 arc-min of the bulge in the low-extinction (Aᵥ = 0.8 mag) Plaut field at l= 0 deg, b= -8 deg, approximately 1 kpc south of the nucleus. This is the point at which the transition between bulge and halo populations likely occurs and is, therefore, an excellent location to study the interface between the dense metal-rich bulge and the metal-poor halo. In this conference we report results based on three first-epoch and three second-epoch plates spanning 21 years. It is found that it is possible to obtain proper-motions with errors less than 0.5 mas/yr for a substantial number of stars down to V= 20, without color restriction. For the subsample with errors less than 1 mas/yr we derive proper-motion dispersions in the direction of Galactic longitude and latitude of 3.378 +/- 0.033 mas/yr and 2.778 +/- 0.028 mas/yr respectively. These dispersions agree with those derived by Spaenhauer et al. (1992) in Baade's window.