Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars
Michelle Kunimoto, Jaymie M. Matthews
Abstract
Abstract We present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0.5 and 16 R ⊕ and orbital periods between 0.78 and 400 days orbiting FGK dwarf stars. We base our results on an independent planet catalog compiled from our search of all ∼200,000 stars observed over the Kepler mission, with precise planetary radii supplemented by Gaia DR2-incorporated stellar radii. We take into account detection and vetting efficiency, planet radius uncertainty, and reliability against transit-like noise signals in the data. By analyzing our FGK occurrence rates as well as those computed after separating F-, G-, and K-type stars, we explore dependencies on stellar effective temperature, planet radius, and orbital period. We reveal new characteristics of the photoevaporation-driven “radius gap” between ∼1.5 and 2 R ⊕ , indicating that the bimodal distribution previously revealed for P < 100 days exists only over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, we provide several estimates of the “eta-Earth” value—the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0.75–1.5 R ⊕ orbiting in a conservatively defined habitable zone (0.99–1.70 au) around G-type stars, we place an upper limit (84.1th percentile) of <0.18 planets per star.