Improved parameters of seven Kepler giant companions characterized with SOPHIE and HARPS-N
Authors:
Bonomo et al
Abstract:
Radial-velocity observations of Kepler candidates obtained with the SOPHIE and HARPS-N spectrographs have permitted unveiling the nature of the five giant planets Kepler-41b, Kepler-43b, Kepler-44b, Kepler-74b, and Kepler-75b, the massive companion Kepler-39b, and the brown dwarf KOI-205b. These companions were previously characterized with long-cadence (LC) Kepler data. Here we aim at refining the parameters of these transiting systems by i) modelling the published radial velocities (RV) and Kepler short-cadence (SC) data that provide a much better sampling of the transits, ii) performing new spectral analyses of the SOPHIE and ESPaDOnS spectra, and iii) improving stellar rotation periods hence stellar age estimates through gyrochronology, when possible. Posterior distributions of the system parameters were derived with a differential evolution Markov chain Monte Carlo approach. Our main results are as follows: a) Kepler-41b is significantly larger and less dense than previously found because a lower orbital inclination is favoured by SC data. This also affects the determination of the geometric albedo that is lower than previously derived: Ag less than 0.135; b) Kepler-44b is moderately smaller and denser than reported in the discovery paper; c) good agreement was achieved with published Kepler-43, Kepler-75, and KOI-205 system parameters, although the host stars Kepler-75 and KOI-205 were found to be slightly richer in metals and hotter, respectively; d) the previously reported non-zero eccentricities of Kepler-39b and Kepler-74b might be spurious. If their orbits were circular, the two companions would be smaller and denser than in the eccentric case. The radius of Kepler-39b is still larger than predicted by theoretical isochrones. Its parent star is hotter and richer in metals than previously determined.
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).
