The atmospheres of the hot-Jupiters Kepler-5b and Kepler-6b observed during occultations with Warm-Spitzer and Kepler

Abstract

This paper reports the detection and the measurements of occultations of the two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent stars. The observations are obtained in the near infrared with Spitzer Space Telescope and at optical wavelengths by combining more than a year of Kepler photometry. The investigation consists of constraining the eccentricities of these systems and of obtaining broad band emergent spectra for individual planets. For both targets, the occultations are detected at 3 sigma level at each wavelength with mid-occultation times consistent with circular orbits. The brightness temperatures of these planets are deduced from the infrared observations and reach T=1930+/-100K and T=1660+/-120K for Kepler-5b and Kepler-6b respectively. We measure optical geometric albedos A_g in the Kepler bandpass and find A_g=0.12+/-0.04 for Kepler-5b and A_g=0.11+/-0.04 for Kepler-6b leading to an upper limit for the Bond albedo of A_B < 0.17 in both cases. The observations for both planets are best described by models for which most of the incident energy is redistributed on the dayside, with only less than 10% of the absorbed stellar flux redistributed to the night side of these planets. The data for Kepler-5b favor a model without a temperature inversion, whereas for Kepler-6b they do not allow distinguishing between models with and without inversion.