* Astronomy

Title: Precise radial velocities of giant stars V. A brown dwarf and a planet orbiting the K giant stars tau Gem and 91 Aqr
Authors: D. S. Mitchell, S. Reffert, T. Trifonov, A. Quirrenbach, D. A. Fischer

We aim to detect and characterise 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 have been taken at Lick Observatory. Our survey includes 373 G and K giants. Radial velocity data showing periodic variations are fitted with Keplerian orbits using a chi² minimisation technique. We report the presence of two substellar companions to the K giant stars tau Gem and 91 Aqr. The brown dwarf orbiting tau Gem has an orbital period of 305.5 ± 0.1 days, a minimum mass of 20.6 Jupiter masses, 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 3.2 Jupiter masses, 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.

Read more (1815kb, PDF)