MOA-2009-BLG-387Lb: a massive planet orbiting an M dwarf

V. Batista, A. Gould, S. Dieters, S. Dong, I. Bond, J.~P. Beaulieu, D. Maoz, B. Monard, G.~W. Christie, J. McCormick, M.~D. Albrow, K. Horne, Y. Tsapras, M.~J. Burgdorf, S. Calchi Novati, J. Skottfelt, J. Caldwell, S. Kozlowski, D. Kubas, B.~S. GaudiC. Han, D.~P. Bennett, J. An, MOA Collaboration, F. Abe, C.~S. Botzler, D. Douchin, M. Freeman, A. Fukui, K. Furusawa, J.~B. Hearnshaw, S. Hosaka, Y. Itow, K. Kamiya, P.~M. Kilmartin, A. Korpela, W. Lin, C.~H. Ling, B.~S. Makita, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, M. Nagaya, K. Nishimoto, K. Ohnishi, T. Okumura, Y.~C. Perrott, N. Rattenbury, T. Saito, D.~J. Sullivan, T. Sumi, W.~L. Sweatman, P.~J. Tristram, E. von Seggern, P.~C.~M. Yock, PLANET Collaboration, S. Brillant, J.~J. Calitz, A. Cassan, A. Cole, K. Cook, C. Coutures, D. Dominis Prester, J. Donatowicz, J. Greenhill, M. Hoffman, F. Jablonski, S.~R. Kane, N. Kains, J.-B. Marquette, R. Martin, E. Martioli, P. Meintjes, J. Menzies, E. Pedretti, K. Pollard, K.~C. Sahu, C. Vinter, J. Wambsganss, R. Watson, A. Williams, M. Zub, FUN Collaboration, W. Allen, G. Bolt, M. Bos, D.~L. DePoy, J. Drummond, J.~D. Eastman, A. Gal-Yam, E. Gorbikov, D. Higgins, J. Janczak, S. Kaspi, C.-U. Lee, F. Mallia, A. Maury, L.~A.~G. Monard, D. Moorhouse, N. Morgan, T. Natusch, E.~O. Ofek, B.-G. Park, R.~W. Pogge, D. Polishook, R. Santallo, A. Shporer, O. Spector, G. Thornley, J.~C. Yee, MiNDSTEp Consortium, V. Bozza, P. Browne, M. Dominik, S. Dreizler, F. Finet, M. Glitrup, F. Grundahl, K. Harpsøe, F.~V. Hessman, T.~C. Hinse, M. Hundertmark, U.~G. Jørgensen, C. Liebig, G. Maier, L. Mancini, M. Mathiasen, S. Rahvar, D. Ricci, G. Scarpetta, J. Southworth, J. Surdej, F. Zimmer, RoboNet Collaboration, A. Allan, D.~M. Bramich, C. Snodgrass, I.~A. Steele, R.~A. Street

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Aims. We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M⊙ < Mhost < 0.49 M⊙ at 90% confidence. The planet-star mass ratio q = 0.0132 ± 0.003 has been measured extremely well, so at the best-estimated host mass, the planet mass is mp = 2.6 Jupiter masses for the median host mass, M = 0.19 M⊙. Methods. The host mass is determined from two “higher order” microlensing parameters. One of these, the angular Einstein radius θE = 0.31 ± 0.03 mas has been accurately measured, but the other (the microlens parallax πE, which is due to the Earth’s orbital motion) is highly degenerate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. Results. The 90% confidence intervals for the distance, semi-major axis, and period of the planet are 3.5 kpc < DL < 7.9 kpc, 1.1 AU < a < 2.7 AU, and 3.8 yr < P < 7.6 yr, respectively.
Original languageEnglish
Pages (from-to)A102
Number of pages16
JournalAstronomy and Astrophysics
Early online date12 Apr 2011
Publication statusPublished - 1 May 2011


  • gravitational lensing: micro, methods: data analysis, planets and satellites: detection, methods: numerical, instrumentation: adaptive optics, instrumentation: photometers

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