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

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American Astronomical Society
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Abstract

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_P sin i = 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_☉. 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_☉) with known planets. All nine planets orbit at distances ɑ ≥ 0.78 AU, which is significantly different from the semimajor axis distribution of planets around lower mass stars.

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