Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.4687m&link_type=abstract
HST Proposal ID #4687
Astronomy and Astrophysics
Astronomy
Hst Proposal Id #4687 Cool Stars Astrometry
Scientific paper
This is the third cycle of a 3-year program to determine the parallaxes and proper motions of stars having the most extreme velocities known in the galactic rest frame. Such stars constrain the local galactic escape velocity and thus are important for estimating the mass distribution in the galactic disk. The currently accepted value of V(esc) is around 475 k/s (Cudworth 1990), however this result is based on distances dependent on uncertain photometric corrections and reddening estimates. The derived photometric distances for these stars are in the range 180 to 330 pc, so the parallaxes are in the range 3 to 6 milliarsec. If these distances are approximately correct, it will be possible to measure them at the 4-sigma level using the FGS on the HST if care is taken with the observations and reductions. Cudworth has pointed out that even a 10% change in V(esc) produces a significant effect (> 50%) change in the derived galactic mass. Therefore, it is of considerable interest to have reliable distances, hence space vel- ocities, for these stars.
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