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

By J. Johnson, Debra A. Fischer, G. Marcy, Jason T. Wright, Peter Edward Driscoll, R. P. Butler, S. Hekker, S. Reffert, S. Vogt. 2007

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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 MJ in a 351.5 day orbit around HD 192699, a planet with a minimum mass of 2.0 MJ in a 341.1 day orbit around HD 210702, and a planet with a minimum mass of 0.61 MJ 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 a ≥ 0.78 AU, which is significantly different from the semimajor axis distribution of planets around lower mass stars.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cbfceb1e629551ca56fead8f8beb2cd49adce552

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Stellar Parameters and Elemental Abundances of Late-G Giants (2008, unknown): “…planets: HD 104985 (Sato et al. 2003); HD 62509 (Reffert et al. 2006; Hatzes et al. 2006); HD 28305 (Sato et al. 2007); HD 142091, HD 167042, and HD 210702 (Johnson et al. 2007; Sato et al., in preparation); HD 1073832 (Liu et al. 2008); HD 81688, HD 188310, and HD 199665 (Sato et al. 2008).”
A New Planet around an M Dwarf: Revealing a Correlation between Exoplanets and Stellar Mass (2007, background): “At higher stellar masses we are conducting a search for planets around intermediate–mass subgiants at Lick and Keck Observatories (Johnson et al. 2006a, 2007).”
THE FREQUENCY OF HOT JUPITERS ORBITING NEARBY SOLAR-TYPE STARS (2012, background): “…to monitor low-mass stars (the Keck M-dwarf survey and M2K; Johnson et al. 2010c; Apps et al. 2010), intermediate mass stars (“Retired A Stars”; Johnson et al. 2007), high metallicity stars (N2K; Fischer et al. 2005), active stars, SIM reference stars, Kepler targets, systems discovered by…”
Precise radial velocities of giant stars. III. Spectroscopic stellar parameters (2007, background): “…Prieto & Lambert (1999), we estimate a typical mass of 2.0 M⊙ for our sample, with the bulk of the field giant sample in the range 1.4 - 2.9 M⊙ (first to third quartiles), which is the typical range covered by companion hosting giants according to Sadakane et al. (2005) and Johnson et al. (2007).”
THE CALIFORNIA PLANET SURVEY. I. FOUR NEW GIANT EXOPLANETS (2010, background): “Remarkably, the exoplanets exhibit a sharp rise in occurrence beyond 1AU (Johnson et al. 2007b; Cumming et al. 2008), indicating a great population of giant planets resides there.”
Extrasolar planets and brown dwarfs around A-F type stars. VI. High precision RV survey of early type dwarfs with HARPS (2008, background): “…to study “retired” early-type instead, either low-mass (≤1.6 M ) giants, intermediate-mass (1.6−2 M ) subgiants, or clump giants (1.7−3.9 M ) (see e.g., Hatzes et al. 2005; Niedzielski et al. 2007; Johnson et al. 2006, 2007; Lovis & Mayor 2007; Article published by EDP Sciences Sato et al. 2008).”
THE RUNTS OF THE LITTER: WHY PLANETS FORMED THROUGH GRAVITATIONAL INSTABILITY CAN ONLY BE FAILED BINARY STARS (2009, background): “In addition, other A-stars host planets at 1–2 AU (Johnson et al. 2007) which, although they have a distinct semi-major axis distribution from planets orbiting G and M stars, are likely formed by core accretion.”
RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS–PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS (2009, methodology): “We derive updated orbit solutions using new observations for five of the known planet-hosting IM subgiants in our sample, which were originally announced by Johnson et al. (2007b), Johnson et al. (2008), and Sato et al. (2008b).”
Variations on Debris Disks: Icy Planet Formation at 30-150 AU for 1-3 M☉ Main-Sequence Stars (2008, background): “Because gas giants are common around evolved A stars (Johnson et al. 2007), gas giants probably play a significant role in the evolution of debris disks around A stars.”
Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes (2016, background): “11 These are stars that were targeted by the radial-velocity survey of Johnson et al. (2007) because it was thought that their main-sequence progenitors were massive (M1.”
TEN NEW AND UPDATED MULTIPLANET SYSTEMS AND A SURVEY OF EXOPLANETARY SYSTEMS (2008, background): “This trend, if it is not simply Poisson noise and should hold up as more M-dwarf systems are discovered, is especially surprising since M dwarfs have a lower-than-average planet occurrence rate (Endl et al. 2006; Johnson et al. 2007a; Mayor et al. 2008).”
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs - I. New atmospheric parameters and masses for 48 stars with planets (2013, background): “The most productive radial velocity planet search surveys concentrated their efforts on the search for planets around solar-type, FGK dwarfs or sub-giants (for some examples see e.g. Udry et al. 2000; Mayor et al. 2003; Marcy et al. 2005; Johnson et al. 2007b).”
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CHROMOSPHERIC ACTIVITY AND JITTER MEASUREMENTS FOR 2630 STARS ON THE CALIFORNIA PLANET SEARCH (2010, methodology): “Chromospheric activity is monitored in the stellar spectra used to derive precision radial velocities for stars on many Doppler planet searches (Saar, Butler, Marcy 1998; Saar & Fischer 1999; Paulson et al. 2002; Wright et al. 2004; Wright 2005; Johnson et al. 2007).”
THE ORBITAL EVOLUTION OF GAS GIANT PLANETS AROUND GIANT STARS (2009, background): “One of the most important trends that these surveys have revealed is the lack of close-in planets orbiting stars with masses M > 1.5 M (Johnson et al. 2007b; Sato et al. 2008; Wright et al. 2009) despite the fact that these planets are found around ≈20% of the main-sequence (MS) stars with M < 1.2…”
Limits on Planetary Companions from Doppler Surveys of Nearby Stars (2016, background): “…Search was expanded over the years with bright stars added from the original Lick program as it winded down, as well as large samples of subgiants (Johnson et al. 2007), metal-rich main sequence stars (Fischer et al. 2005; Robinson et al. 2007), young stars (Hillenbrand et al. 2014), and other…”
Planet Formation around Stars of Various Masses: The Snow Line and the Frequency of Giant Planets (2007, background): “Though sample numbers are small, it appears that observable gas giant frequency increases with stellar mass across a wide range of host masses (Johnson et al. 2007a).”