On the Low False Positive Probabilities of Kepler Planet Candidates

Abstract

We present a framework to conservatively estimate the probability that any particular planet-like transit signal observed by the Kepler mission is in fact a planet, prior to any ground-based follow-up efforts. We use Monte Carlo methods based on stellar population synthesis and Galactic structure models, and report a priori false positive probabilities for every Kepler Object of Interest in tabular form, assuming a 20% intrinsic occurrence rate of close-in planets in the radius range 0.5 Rearth < Rp < 20 Rearth. Almost every candidate has FPP <10%, and over half have FPP <5%. This probability varies most strongly with the magnitude and Galactic latitude of the Kepler target star, and more weakly with transit depth. We establish that a single deep high-resolution image will be an extremely effective follow-up tool for the shallowest (Earth-sized) transits, providing the quickest route towards probabilistically "validating" the smallest candidates by potentially decreasing the false positive probability of an earth-sized transit around a faint star from >10% to <1%. On the other hand, we show that the most useful follow-up observations for moderate-depth (super-Earth and Neptune-sized) candidates are shallower AO imaging and high S/N spectroscopy. Since Kepler has detected many more planetary signals than can be positively confirmed with ground-based follow-up efforts in the near term, these calculations will be crucial to using the ensemble of Kepler data to determine population characteristics of planetary systems. We also describe how our analysis complements the Kepler team's more detailed BLENDER false positive analysis for planet validation.