On the detection of Exomoons: A search in Kepler data for the orbital sampling effect and the scatter peak

Abstract

Despite the discovery of thousands of exoplanets, no exomoons have been detected so far. We test a recently developed method for exomoon search, the orbital sampling effect (OSE), using the full exoplanet photometry from the Kepler Space Telescope. The OSE is applied to phase-folded transits, for which we present a framework to detect false positives, and discuss four candidates which pass several of our tests. Using numerical simulations, we inject exomoon signals into real Kepler data and retrieve them, showing that under favorable conditions, exomoons can be found with Kepler and the OSE method. In addition, we super-stack a large sample of Kepler planets to search for the average exomoon OSE and the accompanying increase in noise, the scatter peak. We find a significant OSE-like signal, which might indicate the presence of moons, for planets with 35d<P<80d, having an average dip per planet of 6+-2ppm, corresponding to a moon radius of 2120 +330 -370km for the average star radius of 1.24R_Sun in this sample.