1212.4853 (Subo Dong et al.)

Fast Rise of "Neptune-Size" Planets (4-8 R_Earth) from P~10 to ~250 days -- Statistics of Kepler Planet Candidates Up to ~0.75 AU    [PDF]

Subo Dong, Zhaohuan Zhu

We infer period (P) and size (R_p) distribution of Kepler transiting planet candidates with R_p> 1 R_Earth and P<250 days hosted by solar-type stars. The planet detection efficiency is computed by using measured noise and the observed timespans of the light curves for ~120,000 Kepler target stars. Given issues with the parameters of Kepler host stars and planet candidates (especially the unphysical impact parameter distribution reported for the candidates), we focus on deriving the shape of planet period and radius distribution functions. We find that for orbital period P>10 days, the planet frequency dN_p/d logP for "Neptune-size" planets (R_p = 4-8 R_Earth) increases with period as \propto P^{0.7\pm0.1}. In contrast, dN_p/dlogP for Super-Earth-Size (2-4 R_Earth) as well as Earth-size (1-2 R_Earth) planets are consistent with a nearly flat distribution as a function of period (\propto P^{0.11\pm0.05}) and \propto P^{-0.10\pm0.12}, respectively), and the normalizations are remarkably similar (within a factor of ~ 1.5). The shape of the distribution function is found to be not sensitive to changes in selection criteria of the sample. The implied nearly flat or rising planet frequency at long period appears to be in tension with the sharp decline at ~100 days in planet frequency for low mass planets (planet mass m_p < 30 M_Earth) recently suggested by the HARPS survey.

View original: http://arxiv.org/abs/1212.4853