The hot-Jupiter Kepler-17b: Discovery, obliquity from stroboscopic starspots, and atmospheric characterization

J.-M. Désert, D. Charbonneau, S. Ballard, J.A. Carter, S.N. Quinn, F. Fressin, D.W. Latham, G. Torres, J.J. Lissauer, D.D. Sasselov, B.-O. Demory, S. Seager, J.N. Winn, J.J. Fortney, D.C. Fabrycky, W.D. Cochran, M. Endl, P.J. MacQueen, H.T. Isaacson, H.A. KnutsonG.W. Marcy, L.A. Buchhave, S.T. Bryson, J.F. Rowe, W.J. Borucki, J.L. Christiansen, M.R. Haas, D. Koch, N.M. Batalha, T.M. Brown, D.A. Caldwell, J.M. Jenkins, F. Mullally, P. Tenenbaum, D. Deming, E.B. Ford, R.L. Gilliland, M. Gillon, K. Kinemuchi, M. Still, P.W. Lucas, K. Uddin

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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 m s. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T = 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 ± 0.03R . We estimate the planet mass and radius to be M = 2.45 0.11 M and R = 1.31 ± 0.02R . 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 = 1880 ± 100 K and = 1770 ± 150 K. We measure the optical geometric albedo A in the Kepler bandpass and find A = 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.
Original languageEnglish
Article number14
Number of pages21
JournalAstrophysical Journal, Supplement Series
Issue number1
Publication statusPublished - 1 Nov 2011


  • planetary systems
  • stars: individual (Kepler-17b, KIC 10619192, 2MASS 19533486+4748540)
  • eclipses
  • techniques: photometry


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