Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of β Geminorum

Our aim is to confirm the nature of the long period radial velocity measurements for β Gem first found by Hatzes & Cochran (1993). We present precise stellar radial velocity measurements for the K giant star β Gem spanning over 25 years. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry was also made to discern the true nature of the long period radial velocity variations. The radial velocity data show that the long period, low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. Furthermore, the Ca II K emission, spectral line bisectors, and Hipparcos photometry show no significant variations of these quantities with the radial velocity period. An orbital solution assuming a stellar mass of 1.7 M⊙ yields a period, P = 589.6 days, a minimum mass of 2.3 MJupiter, and a semi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02). The data presented here confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). β Gem is the sixth intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.