Contamination in the Kepler Field. Identification of 685 KOIs as False Positives Via Ephemeris Matching Based On Q1-Q12 Data

摘要

The Kepler mission has to date found almost 6,000 planetary transit-likesignals, utilizing three years of data for over 170,000 stars at extremely highphotometric precision. Due to its design, contamination from eclipsingbinaries, variable stars, and other transiting planets results in a significantnumber of these signals being false positives. This directly affects thedetermination of the occurrence rate of Earth-like planets in our Galaxy, aswell as other planet population statistics. In order to detect as many of thesefalse positives as possible, we perform ephemeris matching among all transitingplanet, eclipsing binary, and variable star sources. We find that 685 KeplerObjects of Interest - 12% of all those analyzed - are false positives as aresult of contamination, due to 409 unique parent sources. Of these, 118 havenot previously been identified by other methods. We estimate that ~35% of KOIsare false positives due to contamination, when performing a first-ordercorrection for observational bias. Comparing single-planet candidate KOIs tomulti-planet candidate KOIs, we find an observed false positive fraction due tocontamination of 16% and 2.4% respectively, bolstering the existing evidencethat multi-planet KOIs are significantly less likely to be false positives. Wealso analyze the parameter distributions of the ephemeris matches and derive asimple model for the most common type of contamination in the Kepler field. Wefind that the ephemeris matching technique is able to identify lowsignal-to-noise false positives that are difficult to identify with othervetting techniques. We expect false positive KOIs to become more frequent whenanalyzing more quarters of Kepler data, and note that many of them will not beable to be identified based on Kepler data alone.