Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants

We report precision Doppler measurements of three intermediate-mass subgiants obtained at Lick and Keck Observatories. All three stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. We find a planet with a minimum mass M_Psini=2.5 M_J in a 351.5 day orbit around HD 192699, a planet with a minimum mass of 2.0 M_J in a 341.1 day orbit around HD 210702, and a planet with a minimum mass of 0.61 M_J in a 297.3 day orbit around HD 175541. Mass estimates from stellar interior models indicate that all three stars were formerly A-type, main-sequence dwarfs with masses ranging from 1.65 to 1.85 M_solar. These three long-period planets would not have been detectable during their stars' main-sequence phases due to the large rotational velocities and stellar jitter exhibited by early-type dwarfs. There are now nine ``retired'' (evolved) A-type stars (M_*>1.6 M_solar) with known planets. All nine planets orbit at distances a>=0.78 AU, which is significantly different from the semimajor axis distribution of planets around lower mass stars.

Based on observations obtained at the Lick Observatory, which is operated by the University of California, and W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.