Accounting for incompleteness due to transit multiplicity in Kepler planet occurrence rates

Abstract

We investigate the role that planet detection order plays in the Kepler planet detection pipeline. The Kepler pipeline typically detects planets in order of descending signal strength (MES). We find that the detectability of transits experiences an additional 5.5 per cent and 15.9 per cent efficiency loss, for periods <200 days and >200 days respectively, when detected after the strongest signal transit in a multiple-planet system. We provide a method for determining the transit probability for multiple-planet systems by marginalizing over the empirical Kepler dataset. Furthermore, because detection efficiency appears to be a function of detection order, we discuss the sorting statistics that affect the radius and period distributions of each detection order. Our occurrence rate dataset includes radius measurement updates from the California Kepler Survey (CKS), Gaia DR2, and asteroseismology. Our population model is consistent with the results of Burke et al. (2015), but now includes an improved estimate of the multiplicity distribution. From our obtained model parameters, we find that only 4.0±4.6 per cent of solar-like GK dwarfs harbour one planet. This excess is smaller than prior studies and can be well modelled with a modified Poisson distribution, suggesting that the Kepler Dichotomy can be accounted for by including the effects of multiplicity on detection efficiency. Using our modified Poisson model, we expect the average number of planets is 5.86 ± 0.18 planets per GK dwarf within the radius and period parameter space of Kepler.