A closer look at planet occurrence rates: AO follow-up of 71 stars in the Kepler field

One of the core goals of the Kepler mission was to determine the frequency of Earth-like planets that orbit Sun-like stars. Accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stellar target search sample. Previous ground-based follow-up observations have, through a variety of methods, sought to better our knowledge of those stars that are known to host planets. Kepler stars without detected planets, however, have as of yet not been examined as closely with respect to exoplanet occurrence. In this presentation, we better constrain stellar multiplicity for stars around which Kepler could have theoretically detected a transiting Earth-sized planet in the habitable zone. We subsequently aim to improve estimates of eta_Earth — the frequency of potentially habitable, Earth-sized planets — with our data. With adaptive optics observations of 71 stars from the Shane 3-m telescope at Lick Observatory, we report 14 stellar companions within 4″ of 13 Kepler target stars. Of these companions, we determine through multiple independent methods that 7 stellar companions are likely to be bound to their primary. We then extrapolate the results of this study to adjust the input stellar sample to Kepler's publicly available DR25 products, flagging and removing stars on a probabilistic basis as determined by our observed multiplicity rate. In doing so, we find that the occurrence rate of potentially Earth-like planets orbiting GK stars is roughly 14% higher than previously calculated. In addition to informing occurrence estimates, the multiplicity results from this study can be used in further investigations into the architectures of planetary systems orbiting stars with stellar companions.