The Galactic Bulge Velocity Dispersion As Measured By Stellar Proper Motions In Plaut'S Window

We have begun an investigation at Plant's low extinction window, located at (l,b)=(0,-8), i.e., at the interface between the bulge and the halo. We use 43 scanned photographic plates which cover around 25' x 25'. These plates were taken through five different telescopes over 21 years of time in order to get a deep and large catalog of relative proper motions of the Galactic bulge. Particular attention was paid to the correction of optical field-angle distortion and to differential atmospheric color refraction. The analysis is further complicated by the relatively poor image quality and high degree of crowding on these plates. The photometric data have been partially reduced and will be used in combination with 2MASS infrared data to photometrically segregate the bulge stars from the disk ones. Thus, relatively clean samples will be provided for the study of the bulge's kinematical properties. From the 60,000 stars measured, a subset of similar to 3,000 stars with high precision proper motions and V > 18 mag was selected as probable bulge members. This subsample yields a proper motion dispersion of 3.12 mas/yr and 2.82 mas/yr in galactic longitude and latitude, respectively.