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Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler

Howard, Andrew W. and Ciardi, David and Johnson, John Asher (2012) Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler. Astrophysical Journal Supplement Series, 201 (2). Art. No. 15. ISSN 0067-0049.

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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_*/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 K_p < 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 = k_(R)R^α with k_R = 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).

Item Type:Article
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Howard, Andrew W.0000-0001-8638-0320
Ciardi, David0000-0002-5741-3047
Johnson, John Asher0000-0001-9808-7172
Additional Information:© 2012 American Astronomical Society. Received 2011 March 16; accepted 2012 May 8; published 2012 June 25. 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. We thank E. Chiang and H. Knutson for helpful conversations. We gratefully acknowledge D. Monet and many other members of the Kepler team. We thank the W. M. Keck Observatory, and both NASA and the University of California for the use of the Keck telescope. We are grateful to the Keck technical staff, especially S. Dahm, H. Tran, and G. Hill for the support of Keck instrumentation, and R. Kibrick, G.Wirth, R. Goodrich for the support of remote observing.We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. G.M. acknowledges NASA grant NNX06AH52G. J.C.-D. acknowledges support from the National Center for Atmospheric Research, which is sponsored by the National Science Foundation. Funding for the Kepler Discovery mission is provided by NASA’s Science Mission Directorate.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:planetary systems; stars: statistics; techniques: photometric
Issue or Number:2
Record Number:CaltechAUTHORS:20121107-110242929
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Official Citation:Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler Andrew W. Howard et al. 2012 ApJS 201 15
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35330
Deposited By: Jason Perez
Deposited On:07 Nov 2012 21:50
Last Modified:09 Mar 2020 13:18

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