Retired a Stars and Their Companions. III. Comparing the Mass–Period Distributions of Planets Around A-Type Stars and Sun-Like Stars

Creators: Bowler, Brendan P.; Johnson, John Asher; Marcy, Geoffrey W.; Henry, Gregory W.; Peek, Kathryn M. G.; Fischer, Debra A.; Clubb, Kelsey I.; Liu, Michael C.; Reffert, Sabine; Schwab, Chirstian; Lowe, Thomas B.

Abstract

We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ≾ M_*/M_☉ ≾ 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26^(+9)_(–8)%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M_(Jup) within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M^α P^β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.

Additional Information

© 2010 American Astronomical Society. Received 2009 June 10; accepted 2009 December 3; published 2009 December 31. Based on observations obtained at the Lick Observatory, which is operated by the University of California. We thank the referee for their helpful comments on this article. We extend our gratitude to the many CAT observers who have helped with this project over the years, including Chris McCarthy, Raj Sareen, Howard Isaacson, Joshua Goldston, BernieWalp, Julia Kregenow, JasonWright, and Shannon Patel. We also gratefully acknowledge the efforts and dedication of the Lick Observatory staff, and the time assignment committee of the University of California for their generous allocations of observing time. B.P.B. thanks Chris Beaumont and Eric Ford for productive discussions about MCMC techniques. J.A.J. is an NSF Astronomy and Astrophysics Postdoctoral Fellow and acknowledges support from the NSF grant AST-0757887. We appreciate funding from NASA grant NNG05GK92G (to G.W.M.). G.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the state of Tennessee through its Centers of Excellence program. D.A.F. is a Cottrell Science Scholar of Research Corporation and acknowledges support from NASA grant NNG05G164G that made thiswork possible. This research made use of the SIMBAD database operated at CSD, Strasbourg France, and the NASA ADS database.

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