August
2012
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2012ApJS..201...15H
Authors
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Howard, Andrew W.
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Marcy, Geoffrey W.
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Bryson, Stephen T.
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Jenkins, Jon M.
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Rowe, Jason F.
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Batalha, Natalie M.
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Borucki, William J.
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Koch, David G.
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Dunham, Edward W.
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Gautier, Thomas N., III
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Van Cleve, Jeffrey
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Cochran, William D.
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Latham, David W.
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Lissauer, Jack J.
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Torres, Guillermo
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Brown, Timothy M.
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Gilliland, Ronald L.
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Buchhave, Lars A.
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Caldwell, Douglas A.
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Christensen-Dalsgaard, Jørgen
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Ciardi, David
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Fressin, Francois
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Haas, Michael R.
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Howell, Steve B.
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Kjeldsen, Hans
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Seager, Sara
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Rogers, Leslie
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Sasselov, Dimitar D.
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Steffen, Jason H.
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Basri, Gibor S.
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Charbonneau, David
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Christiansen, Jessie
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Clarke, Bruce
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Dupree, Andrea
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Fabrycky, Daniel C.
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Fischer, Debra A.
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Ford, Eric B.
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Fortney, Jonathan J.
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Tarter, Jill
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Girouard, Forrest R.
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Holman, Matthew J.
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Johnson, John Asher
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Klaus, Todd C.
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Machalek, Pavel
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Moorhead, Althea V.
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Morehead, Robert C.
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Ragozzine, Darin
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Tenenbaum, Peter
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Twicken, Joseph D.
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Quinn, Samuel N.
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Isaacson, Howard
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Shporer, Avi
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Lucas, Philip W.
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Walkowicz, Lucianne M.
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Welsh, William F.
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Boss, Alan
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Devore, Edna
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Gould, Alan
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Smith, Jeffrey C.
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Morris, Robert L.
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Prsa, Andrej
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Morton, Timothy D.
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Still, Martin
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Thompson, Susan E.
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Mullally, Fergal
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Endl, Michael
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MacQueen, Phillip J.
Abstract
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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 ⊕. 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 sstarf/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 ⊕. 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 ⊕) and out to the longest orbital period (50 days, ~0.25 AU) in our study. For P < 50 days, the distribution of planet radii is given by a power law, df/dlog R = kRR α with kR = 2.9+0.5 - 0.4, α = -1.92 ± 0.11, and R ≡ R p/R ⊕. 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 ⊕ 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 ⊕, 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 ⊕ 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).
Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology.
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