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Frequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008

Gould, A. and Kane, S. R. (2010) Frequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008. Astrophysical Journal, 720 (2). pp. 1073-1089. ISSN 0004-637X.

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We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 < log q < –2, corresponding to the range of ice giants to gas giants. We find d^2 N_(pl)/d log q d log s=(0.36 ± 0.15) dex^(-2) at the mean mass ratio q = 5 × 10^(–4) with no discernible deviation from a flat (Öpik's law) distribution in log-projected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification (A>200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

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Kane, S. R.0000-0002-7084-0529
Additional Information:© 2010 The American Astronomical Society. Received 2010 January 5; accepted 2010 July 8; published 2010 August 17. Work by A.G. was supported in part by NSF grant AST-0757888 and in part by NASA grant 1277721 issued by JPL/Caltech. Work by S.D. was performed under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. This work was supported in part by an allocation of computing time from the Ohio Supercomputer Center. The OGLE project is partially supported by the Polish MNiSW grant N20303032/4275 to AU. The MOA collaboration was supported by the Marsden Fund of New Zealand. The MOA collaboration and a part of authors are supported by the Grant-in-Aid for Scientific Research, JSPS Research fellowships and the Global COE Program “Quest for Fundamental Principles in the Universe” from JSPS and MEXT of Japan. T.S. acknowledges support from grants JSPS18749004, JSPS20740104, and MEXT19015005. The RoboNet project acknowledges support from PPARC (Particle Physics and Astronomy Research Council) and STFC (Science and Technology Facilities Council). C.H. was supported by Creative Research Initiative Program (2009-0081561) of National Research Foundation of Korea. AGY’s activity is supported by a Marie Curie IRG grant from the EU, and by the Minerva Foundation, Benoziyo Center for Astrophysics, a research grant from Peter and Patricia Gruber Awards, and the William Z. and Eda Bess Novick New Scientists Fund at the Weizmann Institute. D.P.B. was supported by grants AST-0708890 from the NSF and NNX07AL71G from NASA. Work by S.K. was supported at the Technion by the Kitzman Fellowship and by a grant from the Israel-Niedersachsen collaboration program. Mt Canopus observatory is financially supported by Dr. David Warren.
Funding AgencyGrant Number
NASA Sagan Fellowship ProgramUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)JSPS18749004
Japan Society for the Promotion of Science (JSPS)JSPS20740104
Ministry of Education, Culture, Sports, Science and Technology (MEXT) of JapanMEXT19015005
National Research Foundation of Korea Creative Research Initiative Program2009-0081561
Minerva FoundationUNSPECIFIED
Benoziyo Center for AstrophysicsUNSPECIFIED
Peter and Patricia Gruber AwardsUNSPECIFIED
Weizmann Institute William Z. and Eda Bess Novick New Scientists FundUNSPECIFIED
Technion Kitzman FellowshipUNSPECIFIED
Israel-Niedersachsen collaboration programUNSPECIFIED
Subject Keywords:gravitational lensing: micro; planetary systems
Issue or Number:2
Classification Code:PACS: 97.82.-j; 97.20.Jg; 97.10.Nf; 95.30.Sf
Record Number:CaltechAUTHORS:20100929-075954088
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Official Citation:A. Gould et al 2010 ApJ 720 1073 doi: 10.1088/0004-637X/720/2/1073
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20212
Deposited By: Ruth Sustaita
Deposited On:30 Sep 2010 15:59
Last Modified:03 Oct 2019 02:07

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