Probing the Atmospheres of KOI-13b, HAT-P-7b & Kepler-43b

Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry

Authors:

Esteves et al

Absrtact:

We present a comprehensive analysis of planetary phase variations, including possible planetary light offsets, using eighteen quarters of data from the Kepler space telescope. After correcting for systematics, we found fourteen systems with significant detections in each of the phase curve components: planet's phase function, secondary eclipse, Doppler boosting and ellipsoidal variations. We model the full phase curve simultaneously, including primary and secondary transits, and derive albedos, day- and night-side temperatures and planet masses. We find that KOI-13b, with a small eccentricity, is the only planet for which an eccentric orbit is favored. We detect a third harmonic with an amplitude of 1.9 ppm for HAT-P-7b for the first time, and confirm the third harmonic for KOI-13b reported in Esteves et al. (2013): both could be due to their spin-orbit misalignments. We also performed a bootstrap analysis of each of our targets, and conclude that the photometric variations of Kepler-43b are not of planetary origin but instead a result of stellar variability and/or residual systematics. For seven planets, we find that the planetary light peak is offset from the substellar point: of those, the hottest two exhibit shifts eastward or to the evening-side, while the cooler five peak westward or on the morning-side. Our findings dramatically increase the number of Kepler planets with detected planetary light offsets, and provide the first evidence in the Kepler data for a correlation between the peak offset direction and the planet's temperature. Such a correlation could arise if thermal emission dominates light from hotter planets that harbor hot spots shifted to the east, as theoretically predicted, while reflected light dominates cooler planets with clouds westward of the substellar point (i.e. on the morning-side).