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TOPIC: Kepler-17b

Blobrana

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Posts: 131433

Date: Oct 8 01:02 2012

Kepler-17	Permalink

Title: Starspot activity and rotation of the planet-hosting star Kepler-17 Authors: Aldo S. Bonomo, Antonino F. Lanza Context. Kepler-17 is a G2V sun-like star accompanied by a transiting planet with a mass of ~2.5 Jupiter masses and an orbital period of 1.486 d, recently discovered by the Kepler space telescope. This star is highly interesting as a young solar analogue. Aims. We used about 500 days of high-precision, high-duty-cycle optical photometry collected by Kepler to study the rotation of the star and the evolution of its photospheric active regions. Methods. We applied a maximum-entropy light curve inversion technique to model the flux rotational modulation induced by active regions that consist of dark spots and bright solar-like faculae with a fixed area ratio. Their configuration was varied after a fixed time interval to take their evolution into account. Active regions were used as tracers to study stellar differential rotation, and planetary occultations were used to constrain the latitude of some spots. Results. Our modelling approach reproduces the light variations of Kepler-17 with a standard deviation of the residuals comparable with the precision of Kepler photometry. We find several active longitudes where individual active regions appear, evolve, and decay with lifetimes comparable to those observed in the Sun, although the star has a spotted area ~10-15 times larger than the Sun at the maximum of the 11-yr cycle. Kepler-17 shows a solar-like latitudinal differential rotation, but the fast spot evolution prevents a precise determination of its amplitude. Moreover, the star shows a cyclic variation of the starspot area with a period of 47.1 ± 4.5 d, particularly evident during the last 200 days of the observations, similar to the solar Rieger cycles. Possible effects of the close-in massive planet on stellar photospheric activity cannot be excluded, but require a long-term monitoring to be unambiguously detected. Read more (716kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jul 29 01:07 2011

Kepler-17b	Permalink

Title: The hot-Jupiter Kepler-17b: discovery, obliquity from stroboscopic starspots, and atmospheric characterisation Authors: Jean-Michel Désert, David Charbonneau, Brice-Olivier Demory, Sarah Ballard, Joshua A. Carter, Jonathan J. Fortney, William D. Cochran, Michael Endl, Samuel N. Quinn, Howard T. Isaacson, Francois Fressin, Lars A. Buchhave, David W. Latham, Heather A. Knutson, Stephen T. Bryson, Guillermo Torres, Jason F. Rowe, Natalie M. Batalha, William J. Borucki, Timothy M. Brown, Douglas A. Caldwell, Jessie L. Christiansen, Drake Deming, Daniel C. Fabrycky, Eric B. Ford, Ronald L. Gilliland, Michaël Gillon, Michaël R. Haas, Jon M. Jenkins, Karen Kinemuchi, David Koch, Jack J. Lissauer, Fergal Mullally, Phillip J. MacQueen, Geoffrey W. Marcy, Dimitar D. Sasselov, Sara Seager, Martin Still, Peter Tenenbaum, Kamal Uddin, Joshua N. Winn This paper reports the discovery and characterisation 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 (HET) show a Doppler signal of 420±15 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 K from high-resolution spectra, we infer a stellar host mass of 1.061±0.067 M_sun and a stellar radius of 1.019±0.033 R_jup. We estimate the planet mass and radius to be Mp=2.450±0.114 M_jup and Rp=1.312±0.018 R_jup and a planet density near 1.35 g.cm-3. 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, 8 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 deg. 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<0.0011). The brightness temperatures of the planet the infrared bandpasses are T_3.6um=1880±100 K and T4.5um=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. Read more (814kb, PDF) __________________

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