A Planetary Companion to the G-Type Giant Star HD 104985

Abstract

We report the detection of a planetary-mass companion to the G9 III giant star HD 104985 from precise Doppler velocity measurements made using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. The radial velocity variability of this star is best explained by an orbital motion with a period of days, a velocity semiamplitude of m s Ϫ1 , and an eccentricity of . 198.2 ‫ע‬ 0.3 161 ‫ע‬ 2 0.03 ‫ע‬ 0.02 Assuming a stellar mass of 1.6 , we obtained a minimum mass and a semimajor axis of 6.3 and 0.78 AU, M M , J respectively, for the companion. A probable upper limit to the stellar mass of 3 yielded , M m sin i p 9.6M , 2 J which falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.