2011ApJS..197...14D

This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope show a Doppler signal of 419.5^+13.3_–15.6 m/s. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T_eff= 5630±100 from high-resolution spectra, we infer a stellar host mass of 1.06±0.07 M_{x2609} and a stellar radius of 1.02±0.03 R_{x2609}. We estimate the planet mass and radius to be M_P= 2.45±0.11 M_J and R_P= 1.31±0.02 R_J. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, eight times the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15°. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e < 0.011). The brightness temperatures of the planet's infrared bandpasses are T_{3.6  µm} = 1880±100 K and T_{4.5  µm} = 1770±150 K. We measure the optical geometric albedo A_g in the Kepler bandpass and find A_g= 0.10±0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side.