Browsing by Subject "stellar activity"

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The Hot-Jupiter Kepler-17b: Discovery, Obliquity from Stroboscopic Starspots, and Atmospheric Characterization
(2011-11) Desert, 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, Francois; 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, Michael; Haas, Michael 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.; Cochran, William D.; Endl, Michael; MacQueen, Phillip J.
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(-15.6)(+13.3) 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-circle dot and a stellar radius of 1.02 +/- 0.03 R-circle dot. 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 degrees. 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.
Precision Radial Velocities With CSHELL
(2011-07) Crockett, Christopher J.; Mahmud, Naved I.; Prato, L.; Johns-Krull, Christopher M.; Jaffe, Daniel T.; Beichman, Charles A.; Jaffe, Daniel T.
Radial velocity (RV) identification of extrasolar planets has historically been dominated by optical surveys. Interest in expanding exoplanet searches to M dwarfs and young stars, however, has motivated a push to improve the precision of near-infrared RV techniques. We present our methodology for achieving 58 m s(-1) precision in the K band on the M0 dwarf GJ 281 using the CSHELL spectrograph at the 3 m NASA Infrared Telescope Facility. We also demonstrate our ability to recover the known 4 M-JUP exoplanet Gl 86 b and discuss the implications for success in detecting planets around 1-3 Myr old T Tauri stars.
A Search For Giant Planet Companions To T Tauri Stars
(2012-12) Crockett, Christopher J.; Mahmud, Naved I.; Prato, L.; Johns-Krull, Christopher M.; Jaffe, Daniel T.; Hartigan, Patrick M.; Beichman, Charles A.; Jaffe, Daniel T.
We present results from an ongoing multiwavelength radial velocity (RV) survey of the Taurus-Auriga star-forming region as part of our effort to identify pre-main-sequence giant planet hosts. These 1-3 Myr old T Tauri stars present significant challenges to traditional RV surveys. The presence of strong magnetic fields gives rise to large, cool star spots. These spots introduce significant RV jitter which can mimic the velocity modulation from a planet-mass companion. To distinguish between spot-induced and planet-induced RV modulation, we conduct observations at similar to 6700 angstrom and similar to 2.3 mu m and measure the wavelength dependence (if any) in the RV amplitude. CSHELL observations of the known exoplanet host Gl 86 demonstrate our ability to detect not only hot Jupiters in the near-infrared but also secular trends from more distant companions. Observations of nine very young stars reveal a typical reduction in RV amplitude at the longer wavelengths by a factor of similar to 2-3. While we cannot confirm the presence of planets in this sample, three targets show different periodicities in the two wavelength regions. This suggests different physical mechanisms underlying the optical and the K-band variability.