A Substellar Companion to the Intermediate‐Mass Giant 11 Comae

Abstract

We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong Station and Okayama Astrophysical Observatory (OAO) reveal Keplerian velocity variations with an orbital period of 326.03 ±0.32days, a semiamplitude of 302.8 ±2.6 ms-1, and an eccentricity of 0.231 ±0.005. Adopting a stellar mass of 2.7 ±0.3 M⊙, the minimum mass of the companion is 19.4 ±1.5 M J, well above the deuterium-burning limit, and the semimajor axis is 1.29 ±0.05 AU. This is the first result from a joint planet-search program between China and Japan aimed at revealing the statistics of substellar companions around intermediate-mass giants. 11 Com b emerged from 300 targets of the planet-search program at OAO. The program's current detection rate of brown dwarf candidates seems to be comparable to the rate of such detections around solar-type stars with orbital separations of ≲3 AU. © 2008. The American Astronomical Society. All rights reserved.