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Published February 20, 2011 | Published
Journal Article Open

A Sub-Saturn Mass Planet, MOA-2009-BLG-319Lb

Abstract

We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K- or M-dwarf star in the inner Galactic disk or Galactic bulge. The high-cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high-magnification event approximately 24 hr prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 ± 0.02) × 10^(–4) and a separation of d = 0.97537 ± 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t_E, and angular Einstein radius, θ_E, along with a standard Galactic model indicates a host star mass of M_L = 0.38^(+0.34)_(–0.18) M_☉ and a planet mass of M_p = 50^(+44)_(–24) M_⊕, which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4^(+1.2)_(–0.6) AU and a distance to the planetary system of D_L = 6.1^(+1.1)_(–1.2) kpc. This separation is ~2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.

Additional Information

© 2011 American Astronomical Society. Received 2010 October 8; accepted 2010 December 8; published 2011 January 28. The MOA project and a part of authors were supported by the Grant-in-Aid for Scientific Research, the grant JSPS20340052, JSPS18253002, JSPS Research fellowships, the Global COE Program of Nagoya University "Quest for Fundamental Principles in the Universe" from JSPS and MEXT of Japan, the Marsden Fund of New Zealand, the New Zealand Foundation for Research and Technology, and grants-in-aid from Massey University and the University of Auckland. N.M. was supported by JSPS Research Fellowships for Young Scientists. T.S. was supported by the grant JSPS20740104. D.P.B. was supported by grants NNX07AL71G and NNX10AI81G from NASA and AST-0708890 from the NSF. A.G. and S.D. were supported in part by NSF AST-0757888. A.G., S.D., S.G., and R.P. were supported in part by NASA NNG04GL51G. Work by S.D. was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. J.C.Y. was supported by an NSF Graduate Research Fellowship. Work by C.H. was supported by the Creative Research Initiative program (2009-0081561) of the National Research Foundation of Korea. Astronomical research at Armagh Observatory was supported by the Department of Culture, Arts, and Leisure (DCAL), Northern Ireland, UK. F.F., D.R., and J.S. acknowledge support from the Communauté française de Belgique—Actions de recherche concertées—Académie universitaire Wallonie-Europe.

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August 22, 2023
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