[ITAL]Hubble Space Telescope[/ITAL] WFPC2 Proper Motions in Two Bulge Fields: Kinematics and Stellar Population of the Galactic Bulge

We report proper motion dispersions for stars in the direction of two fieldsof the Galactic bulge, using HST/WFPC2 images taken six years apart. Our two fields are Baade's Window (l,b)=(1.13,-3.77) and Sgr I (l,b)=(1.25,-2.65). Our proper motion dispersions are in good agreement with prior ground-and space-based proper motion studies in bulge fields, but in contrast to someprior studies, we do not exclude any subset of stars from our studies. InBaade's Window, we find the $l$ and $b$ proper motion dispersions are 2.9 and2.5 mas/yr, while in Sgr I, they are 3.3 and 2.7 mas/yr, respectively. For the first time, we can clearly separate the foreground disk stars outfrom the bulge because of their large mean apparent proper motion. Thepopulation with non-disk kinematics (which we conclude to be the bulge) has anold main sequence turnoff point, similar to those found in old, metal richbulge globular clusters while those stars selected to have disk kinematics lieon a fully populated main sequence. Separating main sequence stars byluminosity, we find strong evidence that the bulge population is rotating,largely explaining observations of proper motion anisotropy in bulge fields.Because we have isolated such a pure sample of stars in the bulge, we have oneof the clearest demonstrations that the old stellar population of the innerbulge/bar is in fact rotating.Comment: To appear in Astronomical Journal; references adde