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

¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
e-mail: msoto@stsci.edu
² Leiden Observatory, Leiden University PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: kuijken@strw.leidenuniv.nl
³ Departamento de Física, Universidad de La Serena, 980 Benavente, La Serena, Chile
⁴ Departamento de Astronomía, Universidad de Chile, 36-D Casilla, Santiago, Chile
e-mail: zeballos@das.uchile.cl
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), an der Sternwarte 16, 14482 Potsdam, Germany
e-mail: akunder@aip.de
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: astraatmadja@mpia.de

Received: 25 May 2011
Accepted: 27 August 2013

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°.