2013A&A...555A..87M

We aim to detect and characterize substellar companions to K giant stars to further our knowledge of planet formation and stellar evolution of intermediate-mass stars. For more than a decade we have used Doppler spectroscopy to acquire high-precision radial velocity measurements of K giant stars. All data for this survey were taken at Lick Observatory. Our survey includes 373 G and K giants. Radial velocity data showing periodic variations were fitted with Keplerian orbits using a χ² minimization technique. We report the presence of two substellar companions to the K giant stars τ Gem and 91 Aqr. The brown dwarf orbiting τ Gem has an orbital period of 305.5±0.1-days, a minimum mass of 20.6M_J, and an eccentricity of 0.031±0.009. The planet orbiting 91 Aqr has an orbital period of 181.4±0.1-days, a minimum mass of 3.2M_J, and an eccentricity of 0.027±0.026. Both companions have exceptionally circular orbits for their orbital distance, as compared to all previously discovered planetary companions.