Proper motions for HST observations in three off-axis bulge fields

Abstract

Aims: This is the second in a series of papers that attempt to unveil the kinematic structure of the Galactic bulge through studying radial velocities and proper motions. We report here ~15 000 new proper motions for three low foreground-extinction off-axis fields of the Galactic bulge.
Methods: Proper motions were derived from a combination of Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) and Advanced Camera for Surveys (ACS) images taken 8 and 9 years apart, and they reach accuracies better than 0.9 mas yr^-1 for more than ~10 000 objects with magnitudes F814W ≤ 24.
Results: The proper motion distributions in these fields are similar to those of Galactic minor axis bulge fields. We observe the rotation of main sequence stars below the turn-off within the Galactic bulge, as in the minor axis fields.
Conclusions: Our stellar proper motions measurements show a significant bulge rotation for fields as far from the Galactic plane as b ≃ -8°.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555.