Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system

摘要

We announce confirmation of Kepler-418b, one of two proposed planets in thissystem. This is the first confirmation of an exoplanet based primarily on thetransit color signature technique. We used the Kepler public data archivecombined with multicolor photometry from the Gran Telescopio de Canarias andradial velocity follow-up using FIES at the Nordic Optical Telescope forconfirmation. We report a confident detection of a transit color signature thatcan only be explained by a compact occulting body, entirely ruling out acontaminating eclipsing binary, a hierarchical triple, or a grazing eclipsingbinary. Those findings are corroborated by our radial velocity measurements,which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also reportthat the host star is significantly blended, confirming the ~10% lightcontamination suspected from the crowding metric in the Kepler light curvemeasured by the Kepler team. We report detection of an unresolved light sourcethat contributes an additional ~40% to the target star, which would not havebeen detected without multicolor photometric analysis. The resultingplanet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the0.94 Rjup measured by the Kepler team. This is the first confirmation of anexoplanet candidate based primarily on the transit color signature,demonstrating that this technique is viable from ground for giant planets. Itis particularly useful for planets with long periods such as Kepler-418b, whichtend to have long transit durations. Additionally, multicolor photometricanalysis of transits can reveal unknown stellar neighbors and binary companionsthat do not affect the classification of the transiting object but can have avery significant effect on the perceived planetary radius.