HST-FGS parallaxes of two high-velocity stars.
MacConnell, D. Jack; Osborn, Wayne H.; Miller, Richard J.
Abstract
Astrometric position measurements with the Hubble Space Telescope's Fine Guidance System have been used to measure the trigonometric parallaxes of two high-velocity stars, R50 = G166-37 and W624 = G16-25. In both cases, the parallaxes are small and confirm large velocities in the galactocentric rest frame. We derive pi_ {abs} = 5.2 +/- 0.7 mas and vrf = 467 kms for R50. The results for W624 are pi_ {abs} = 3.8 +/- 1.0 and vrf = 326 kms with an uncertainty of about 30%. Our results support a value for the galactic escape velocity at the solar distance of about 475 kms.