THE LOCAL GALACTIC ESCAPE VELOCITY REVISITED - IMPROVED PROPER MOTIONS FOR CRITICAL STARS

Improved proper motions have been derived for nine stars critical to the derivation of the local Galactic escape velocity. In most cases, the new proper motions of these stars, and hence their space velocities, are found to be smaller than those that have been used in recent discussions of the escape velocity. The improved proper motions agree much better with previous data from Luyten than with the Lowell survey. Two of these stars have optical companions close enough to have contaminated the available photometry, thus requiring significant corrections to previously derived distances. With these new data, the lower limit on the local Galactic escape velocity is ∼475 km s-1. Assuming a simple model of the Galactic mass distribution then yields a limit on the mass of the Milky Way script M signtotal ≳ 4 × 1011 script M⊙ sign and a limit on the outer radius of the mass distribution Rlimit, ≳ 34 kpc.