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The quadruple system PG 1115+080 is the second gravitational lens with areported measurement of the Hubble constant. In addition to the primary lens,three nearby galaxies are believed to contribute significantly to the lensingpotential. In this paper we report accurate redshifts for all four galaxies andshow that they belong to a single group at z_d = 0.311. This group has verysimilar properties to Hickson's compact groups of galaxies found at lowerredshifts. We briefly discuss implications for the existing lens models andderive H_0 = 52 +/- 14 km/s/Mpc.Comment: revised to use the updated model of Keeton & Kochanek  (astro-ph/9611216) and to correct the velocity dispersion of the group; 10  pages including 2 eps figures and 2 tables. Submitted to the Astronomical  Journa

Keck Spectroscopy of the Gravitational Lens System PG 1115+080: Redshifts of the Lensing Galaxies.