The Hot-Jupiter Kepler-17b: Discovery, Obliquity from Stroboscopic Starspots, and Atmospheric Characterization

November 2011 • 2011ApJS..197...14D

Authors • Désert, Jean-Michel • Charbonneau, David • Demory, Brice-Olivier • Ballard, Sarah • Carter, Joshua A. • Fortney, Jonathan J. • Cochran, William D. • Endl, Michael • Quinn, Samuel N. • Isaacson, Howard T. • Fressin, François • Buchhave, Lars A. • Latham, David W. • Knutson, Heather A. • Bryson, Stephen T. • Torres, Guillermo • Rowe, Jason F. • Batalha, Natalie M. • Borucki, William J. • Brown, Timothy M. • Caldwell, Douglas A. • Christiansen, Jessie L. • Deming, Drake • Fabrycky, Daniel C. • Ford, Eric B. • Gilliland, Ronald L. • Gillon, Michaël • Haas, Michaël R. • Jenkins, Jon M. • Kinemuchi, Karen • Koch, David • Lissauer, Jack J. • Lucas, Philip • Mullally, Fergal • MacQueen, Phillip J. • Marcy, Geoffrey W. • Sasselov, Dimitar D. • Seager, Sara • Still, Martin • Tenenbaum, Peter • Uddin, Kamal • Winn, Joshua N.

Abstract • 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^-1. 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 _⊙ and a stellar radius of 1.02 ± 0.03 R _⊙. 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\, {\mu m}} = 1880 ± 100 K and T_{4.5\, {\mu m}} = 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.

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Jessie Christiansen

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