A Planetary Companion to the Nearby M 4 Dwarf , Gliese 876

Doppler measurements of the M4 dwarf star, Gliese 876, taken at both Lick and Keck Observatory reveal periodic, Keplerian velocity variations with a period of 61 days. The orbital fit implies that the companion has a mass of, M = 2.1 MJUP/ sin i, an orbital eccentricity of, e = 0.27±0.03, and a semimajor axis of, a = 0.21 AU. The planet is the first found around an M dwarf, and was drawn from a survey of 24 such stars at Lick Observatory. It is the closest extrasolar planet yet found, providing opportunities for follow–up detection. The presence of a giant planet on a non-circular orbit, 0.2 AU from a 1/3 M star, presents a challenge to planet formation theory. This planet detection around an M dwarf suggests that giant planets are numerous in the Galaxy. Subject headings: planetary systems – stars: individual (Gliese 876)