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 MP sin i = 2.5 MJup in a 351.5 day orbit around HD192699, a planet with a minimum mass of 2.0MJup in a 341.1 day orbit around HD210702, and a planet with a minimum mass of 0.61 MJup in a 297.3 day orbit around HD175541. Mass estimates from stellar interior models indicate that all three stars were formerly A–type, main–sequence dwarfs with masses ranging from 1.65M⊙ to 1.85M⊙. 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 9 “retired” (evolved) A–type stars (M∗ > 1.6 M⊙) with known planets. All 9 planets orbit at distances a ≥ 0.78 AU, which is significantly different than the semimajor axis distribution of planets around lower–mass stars. We examine 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 Department of Astronomy, University of California, Mail Code 3411, Berkeley, CA 94720 Department of Physics & Astronomy, San Francisco State University, San Francisco, CA 94132 Department of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218 Department of Terrestrial Magnetism, Carnegie Institution of Washington DC, 5241 Broad Branch Rd. NW, Washington DC, 20015-1305 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands ZAH-Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064