Browsing by Subject "hot jupiters"
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Item A Correlation Between The Eclipse Depths Of Kepler Gas Giant Candidates And The Metallicities Of Their Parent Stars(2012-06) Dodson-Robinson, Sarah E.; Dodson-Robinson, Sarah E.Previous studies of the interior structure of transiting exoplanets have shown that the heavy-element content of gas giants increases with host star metallicity. Since metal-poor planets are less dense and have larger radii than metal-rich planets of the same mass, one might expect that metal-poor stars host a higher proportion of gas giants with large radii than metal-rich stars. Here I present evidence for a negative correlation at the 2.3 sigma level between eclipse depth and stellar metallicity in the Kepler gas giant candidates. Based on Kendall's tau statistics, the probability that eclipse depth depends on star metallicity is 0.981. The correlation is consistent with planets orbiting low-metallicity stars being, on average, larger in comparison with their host stars than planets orbiting metal-rich stars. Furthermore, since metal-rich stars have smaller radii than metal-poor stars of the same mass and age, a uniform population of planets should show a rise in median eclipse depth with [M/H]. The fact that I find the opposite trend indicates that substantial changes in the gas giant interior structure must accompany increasing [M/H]. I investigate whether the known scarcity of giant planets orbiting low-mass stars could masquerade as an eclipse depth-metallicity correlation, given the degeneracy between metallicity and temperature for cool stars in the Kepler Input Catalog. While the eclipse depth-metallicity correlation is not yet on firm statistical footing and will require spectroscopic [Fe/H] measurements for validation, it is an intriguing window into how the interior structure of planets and even the planet formation mechanism may be changing with Galactic chemical evolution.Item Detection Of A Third Planet In The HD 74156 System Using The Hobby-Eberly Telescope(2008-01) Bean, Jacob L.; McArthur, Barbara E.; Benedict, G. Fritz; Armstrong, Amber; Bean, Jacob L.; McArthur, Barbara E.; Benedict, G. Fritz; Armstrong, AmberWe report the discovery of a third planetary-mass companion to the G0 star HD 74156. High-precision radial velocity measurements made with the Hobby-Eberly Telescope aided the detection of this object. The best-fit triple-Keplerian model to all the available velocity data yields an orbital period of 347 days and a minimum mass of 0.4 M-Jup for the new planet. We determine revised orbital periods of 51.7 and 2477 days and minimum masses of 1.9 and 8.0 M-Jup, respectively, for the previously known planets. Preliminary calculations indicate that the derived orbits are stable, although all three planets have significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our detection, HD 74156 becomes the eighth normal star known to host three or more planets. Further study of this system's dynamical characteristics will likely give important insight into planet formation and evolutionary processes.Item A Detection Of H Alpha In An Exoplanetary Exosphere(2012-06) Jensen, Adam G.; Redfield, Seth; Endl, Michael; Cochran, William D.; Koesterke, Lars; Barman, Travis; Endl, Michael; Cochran, William D.; Koesterke, LarsWe report on a search for H alpha absorption in four exoplanets. Strong features at H alpha are observed in the transmission spectra of both HD 189733b and HD 209458b. We attempt to characterize and remove the effects of stellar variability in HD 189733b, and along with an empirical Monte Carlo test the results imply a statistically significant transit-dependent feature of (-8.72 +/- 1.48) x 10(-4) integrated over a 16 angstrom band relative to the adjacent continuum. We interpret this as the first detection of this line in an exoplanetary atmosphere. A previous detection of Ly alpha in HD 189733b's atmosphere allows us to calculate an excitation temperature for hydrogen, T-exc = 2.6 x 10(4) K. This calculation depends significantly on certain simplifying assumptions. We explore these assumptions and argue that T-exc is very likely much greater than the radiative equilibrium temperature (the temperature the planet is assumed to be at based on stellar radiation and the planetary distance) of HD 189733b. A large T-exc implies a very low density that is not in thermodynamic equilibrium with the planet's lower atmosphere. We argue that the n = 2 hydrogen required to cause H alpha absorption in the atmosphere is created as a result of the greater UV flux at HD 189733b, which has the smallest orbit and most chromospherically active central star in our sample. Though the overall integration of HD 209458b's transmission spectrum over a wide band is consistent with zero, it contains a dramatic, statistically significant feature in the transmission spectrum with reflectional symmetry. We discuss possible physical processes that could cause this feature. Our remaining two targets (HD 147506b and HD 149026b) do not show any clear features, so we place upper limits on their H alpha absorption levels.Item Non-Detection Of L-Band Line Emission From The Exoplanet HD189733B(2011-02) Mandell, Avi M.; Deming, L. Drake; Blake, Geoffrey A.; Knutson, Heather A.; Mumma, Michael J.; Villanueva, Geronimo L.; Salyk, Colette; Salyk, ColetteWe attempt to confirm bright non-local thermodynamic equilibrium (non-LTE) emission from the exoplanet HD 189733b at 3.25 mu m, as recently reported by Swain et al. based on observations at low spectral resolving power (lambda/delta lambda approximate to 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power lambda/delta lambda = 27, 000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et al. results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2 nu(2) band of water vapor at 300 K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al.Item Planet Occurrence within 0.25 AU of Solar-Type Stars from Kepler(2012-08) Howard, Andrew W.; Marcy, Geoffrey W.; Bryson, Stephen T.; Jenkins, Jon M.; Rowe, Jason F.; Batalha, Natalie M.; Borucki, William J.; Koch, David G.; Dunham, Edward W.; Gautier, Thomas N., III; Van Cleve, Jeffrey; Cochran, William D.; Latham, David W.; Lissauer, Jack J.; Torres, Guillermo; Brown, Timothy M.; Gilliland, Ronald L.; Buchhave, Lars A.; Caldwell, Douglas A.; Christensen-Dalsgaard, Jorgen; Ciardi, David; Fressin, Francois; Haas, Michael R.; Howell, Steve B.; Kjeldsen, Hans; Seager, Sara; Rogers, Leslie; Sasselov, Dimitar D.; Steffen, Jason H.; Basri, Gibor S.; Charbonneau, David; Christiansen, Jessie; Clarke, Bruce; Dupree, Andrea; Fabrycky, Daniel C.; Fischer, Debra A.; Ford, Eric B.; Fortney, Jonathan J.; Tarter, Jill; Girouard, Forrest R.; Holman, Matthew J.; Johnson, John Asher; Klaus, Todd C.; Machalek, Pavel; Moorhead, Althea V.; Morehead, Robert C.; Ragozzine, Darin; Tenenbaum, Peter; Twicken, Joseph D.; Quinn, Samuel N.; Isaacson, Howard; Shporer, Avi; Lucas, Philip W.; Walkowicz, Lucianne M.; Welsh, William F.; Boss, Alan; Devore, Edna; Gould, Alan; Smith, Jeffrey C.; Morris, Robert L.; Prsa, Andrej; Morton, Timothy D.; Still, Martin; Thompson, Susan E.; Mullally, Fergal; Endl, Michael; MacQueen, Phillip J.; Cochran, William D.; Endl, Michael; MacQueen, Phillip J.We report the distribution of planets as a function of planet radius, orbital period, and stellar effective temperature for orbital periods less than 50 days around solar-type (GK) stars. These results are based on the 1235 planets (formally "planet candidates") from the Kepler mission that include a nearly complete set of detected planets as small as 2 R-circle plus. For each of the 156,000 target stars, we assess the detectability of planets as a function of planet radius, R-p, and orbital period, P, using a measure of the detection efficiency for each star. We also correct for the geometric probability of transit, R-star/a. We consider first Kepler target stars within the "solar subset" having T-eff = 4100-6100 K, log g = 4.0-4.9, and Kepler magnitude Kp < 15 mag, i.e., bright, main-sequence GK stars. We include only those stars having photometric noise low enough to permit detection of planets down to 2 R-circle plus. We count planets in small domains of R-p and P and divide by the included target stars to calculate planet occurrence in each domain. The resulting occurrence of planets varies by more than three orders of magnitude in the radius-orbital period plane and increases substantially down to the smallest radius (2 R-circle plus) and out to the longest orbital period (50 days, similar to 0.25 AU) in our study. For P < 50 days, the distribution of planet radii is given by a power law, df/d log R = k(R)R(alpha) with k(R) = 2.9(-0.4)(+0.5), alpha = -1.92 +/- 0.11, and R equivalent to R-p/R-circle plus. This rapid increase in planet occurrence with decreasing planet size agrees with the prediction of core-accretion Formation but disagrees with population synthesis models that predict a desert at super-Earth and Neptune sizes for close-in orbits. Planets with orbital periods shorter than 2 days are extremely rare; for R-p > 2 R-circle plus we measure an occurrence of less than 0.001 planets per star. For all planets with orbital periods less than 50 days, we measure occurrence of 0.130 +/- 0.008, 0.023 +/- 0.003, and 0.013 +/- 0.002 planets per star for planets with radii 2-4, 4-8, and 8-32 R-circle plus, in agreement with Doppler surveys. We fit occurrence as a function of P to a power-law model with an exponential cutoff below a critical period P-0. For smaller planets, P-0 has larger values, suggesting that the "parking distance" for migrating planets moves outward with decreasing planet size. We also measured planet occurrence over a broader stellar T-eff range of 3600-7100 K, spanning M0 to F2 dwarfs. Over this range, the occurrence of 2-4 R-circle plus planets in the Kepler field increases with decreasing T-eff, with these small planets being seven times more abundant around cool stars (3600-4100 K) than the hottest stars in our sample (6600-7100 K).