HST-FGS PARALLAXES OF 2 HIGH-VELOCITY STARS

Astrometric position measurements with the Hobble Space Telescope's Fi ne Guidance System have been used to measure the trigonometric paralla xes of two high-velocity stars, R50=G166-37 and W624=G16-25. In both c ases, the parallaxes are small and confirm large velocities in the gal actocentric rest frame. We derive pi(abs)=5.2+/-0.7 mas and V-RF=467 k m s(-1) for R50. The results for W624 are pi(abs)=3.8+/-1.0 and V-RF=3 26 km s(-1) with an uncertainty of about 30%. Our results support a va lue for the galactic escape velocity at the solar distance of about 47 5 km s(-1). (C) 1997 American Astronomical Society.