HST astrometry: the Galactic constant Theta0/R0
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 = Theta0/R0. We find: Theta0/R0 = 27.4 +/- 1.8 km/s/kpc.
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