A Critical Test of the Galactic Escape Velocity at - of 2428

Details A Critical Test of the Galactic Escape Velocity at - of 2428 A Critical Test of the Galactic Escape Velocity at - of 2428

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.3856m&link_type=abstract

HST Proposal ID #3856

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Hst Proposal Id #3856 Stellar Populations Astrometry

Scientific paper

We propose to measure the trigonometric parallaxes and proper motions of the three high-proper motion stars which Carney, Latham, and Laird (1988) identify as having the most extreme velocities known in the galactic rest frame. Using these stars, they conclude that the local value of the escape velocity, V(esc), is at least 500 k/s, and this leads them to draw other important conclusions regarding the distribution of mass in the galactic disk. However, their assigned distances, and hence the tangential velocities and V(esc) value, depend on uncertain photometric corrections and reddening estimates. The photometric distances they find are in the range 400-550 pc, so the parallaxes are expected to be of the order of 2 milliarcsec. If these distances are approximately correct, it will be possible to measure them at the 4-sigma level using an FGS on the HST. It will be of great interest if the parallaxes are smaller than the estimates of Carney, et al., since this would lead to a higher value for the escape velocity and a larger mass for the galaxy. Alternatively, if the parallaxes are found to be larger than they adopted, either V(esc) is considerably smaller than 500 k/s or these three stars are not the most app- ropriate for setting a limit on V(esc). NOTE added 16-Apr-1991: Three targets changed to two, G166-37 and G233-27. This is Cycle 3 POS mode only. NOTE added 09-Mar-1992: Target G233_27 dropped after TRANS obs. failed due to

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