HST astrometry: the Galactic constant Theta_0/R_0

Abstract

From multi-epoch WFPC2/HST observations we present astrometric measurements of the absolute motion of the bulge stars. The presence of an extragalactic point-source candidate allows us to measure the difference between the Oort constants, A-B = Theta_0/R_0. We find: Theta_0/R_0 = 27.4 +/- 1.8 km/s/kpc.

2 pages, 1 figure, SAIt Padova, 10-12 aprile 2002