2011/08/31 by Eric Gaidos, Debra A. Fischer, Andrew W. Mann +2
Physics and Astronomy · #Astronomy and Astrophysical Research #Habitability of orange dwarf systems #Kepler-47 #Planet #Planetary system #Population #Radial velocity #Scientific Research and Discoveries #Stars #Stellar, planetary, and galactic studies #Terrestrial planet #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/746/1/36
Accepted to the Astrophysical Journal
arxiv created 2011/11/09 · openalex publication_date 2012/01/23 · arxiv updated 2015/05/29 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We constrain the densities of Earth- to Neptune-size planets around very cool ( T e = 3660–4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a model based on Kepler candidate planet radii and a power-law mass–radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov–Smirnov probabilities occur for a power-law index α ≈ 4, indicating that rocky-metal planets dominate the planet population in this size range. A single population of gas-rich, low-density planets with α = 2 is ruled out unless our Doppler errors are ⩾5 m s −1 , i.e., much larger than expected based on observations and stellar chromospheric emission. If small planets are a mix of γ rocky planets (α = 3.85) and 1 − γ gas-rich planets (α = 2), then γ > 0.5 unless Doppler errors are ⩾4 m s −1 . Our comparison also suggests that Kepler 's detection efficiency relative to ideal calculations is less than unity. One possible source of incompleteness is target stars that are misclassified subgiants or giants, for which the transits of small planets would be impossible to detect. Our results are robust to systematic effects, and plausible errors in the estimated radii of Kepler stars have only moderate impact.