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

¹ Probing Lensing Anomalies NETwork (PLANET)  
² Institut d’Astrophysique de Paris, Université Pierre et Marie Curie, CNRS UMR7095, 98bis Boulevard Arago, 75014 Paris, France
e-mail: batista@iap.fr; beaulieu@iap.fr; cassan@iap.fr; marquett@iap.fr
³ Microlensing Follow Up Network ( μ FUN)  
⁴ Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
e-mail: gouldsimkoz@ astronomy.ohio-state.edu; gaudisimkoz@ astronomy.ohio-state.edu; jdeastsimkoz@ astronomy.ohio-state.edu; jyeesimkoz@ astronomy.ohio-state.edu; poggesimkoz@ astronomy.ohio-state.edu; simkoz@ astronomy.ohio-state.edu; nick.morgan@alum.mit.edu
⁵ Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA
e-mail: dong@ias.edu
⁶ Sagan Fellow  
⁷ Microlensing Observations in Astrophysics (MOA)  
⁸ Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland, New Zealand
e-mail: i.a.bond@massey.ac.nz; l.skuljan@massey.ac.nz; w.lin@massey.ac.nz; c.h.ling@massey.ac.nz; w.sweatman@massey.ac.nz
⁹ School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel
e-mail: shai@wise.tau. ac.il; dani@wise.tau. ac.il; david@wise.tau. ac.il; shporer@wise.tau. ac.il; odedspec@wise.tau. ac.il
¹⁰ Bronberg Observatory, Centre for Backyard Astrophysics, Pretoria, South Africa
e-mail: lagmonar@nmisa.org
¹¹ Auckland Observatory, Auckland, New Zealand
e-mail: gwchristie@christie.org.nz
¹² Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland, New Zealand
e-mail: farmcoveobs@xtra.co.nz
¹³ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
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¹⁴ The RoboNet Collaboration  
¹⁵ SUPA School of Physics and Astronomy, Univ. of St Andrews, Scotland KY16 9SS, UK
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¹⁶ Microlensing Network for the Detection of Small Terrestrial Exoplanets (MiNDSTEp)  
¹⁷ Niels Bohr Institutet, Københavns Universitet, Juliane Maries Vej 30, 2100 København Ø, Denmark
¹⁸ Centre for Star and Planet Formation, Københavns Universitet, Øster Voldgade 5-7, 1350 København Ø, Denmark
¹⁹ McDonald Observatory, 16120 St Hwy Spur 78 #2, Fort Davis, TX 79734, USA
e-mail: caldwell@astro.as.utexas.edu
²⁰ European Southern Observatory, Casilla 19001, Santiago 19, Chile
e-mail: sbrillan@eso.org; dkubas@eso.org
²¹ Department of Physics, Institute for Basic Science Research, Chungbuk National University, Chongju 361-763, Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
²² University of Notre Dame, Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556-5670, USA
e-mail: bennett@nd.edu
²³ Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, 464-8601, Japan
e-mail: sumi@stelab.nagoya- u.ac.jp; abe@stelab.nagoya- u.ac.jp; afukui@stelab.nagoya- u.ac.jp; furusawa@stelab.nagoya- u.ac.jp; itow@stelab.nagoya- u.ac.jp; kkamiya@stelab.nagoya- u.ac.jp; kmasuda@stelab.nagoya- u.ac.jp; ymatsu@stelab.nagoya- u.ac.jp; nmiyake@stelab.nagoya- u.ac.jp; mnagaya@stelab.nagoya- u.ac.jp; okumurat@stelab.nagoya- u.ac.jp; sako@stelab.nagoya- u.ac.jp
²⁴ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
e-mail: c.botzler@auckland.ac.nz; p.yock@auckland.ac.nz; yper006@auckland.ac.nz
²⁵ Mt. John Observatory, PO Box 56, Lake Tekapo 8780, New Zealand
²⁶ School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand
e-mail: a.korpela@niwa.co.nz; denis.sullivan@vuw.ac.nz
²⁷ Department of Physics, Konan University, Nishiokamoto 8-9-1, Kobe 658-8501, Japan
²⁸ Nagano National College of Technology, Nagano 381-8550, Japan
²⁹ Tokyo Metropolitan College of Industrial Technology, Tokyo 116-8523, Japan
³⁰ University of the Free State, Faculty of Natural and Agricultural Sciences, Department of Physics, PO Box 339, Bloemfontein 9300, South Africa
e-mail: HoffmaMJ.SCI@mail.uovs.ac.za
³¹ University of Tasmania, School of Mathematics and Physics, Private Bag 37, GPO, Hobart, Tas 7001, Australia
e-mail: John.Greenhill@utas.edu.au; Andrew.Cole@utas.edu.au
³² Lawrence Livermore National Laboratory, Institute of Geophysics and Planetary Physics, PO Box 808, Livermore, CA 94551-0808 USA
e-mail: kcook@llnl.gov
³³ CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
e-mail: coutures@iap.fr
³⁴ Department of Physics, University of Rijeka, Omladinska 14, 51000 Rijeka, Croatia
³⁵ Technische Universitaet Wien, Wieder Hauptst. 8-10, 1040 Wienna, Austria
e-mail: donatowicz@tuwien.ac.at
³⁶ LATT, Université de Toulouse, CNRS, France
³⁷ Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos, SP, Brazil
³⁸ NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 south Wilson Avenue, Pasadena, CA 91125, USA
e-mail: skane@ipac.caltech.edu
³⁹ Perth Observatory, Walnut Road, Bickley, Perth 6076, WA, Australia
e-mail: Ralph.Martin@dec.wa.gov.au; Andrew.Williams@dec.wa.gov.au
⁴⁰ South African Astronomical Observatory, PO box 9, Observatory 7935, South Africa
⁴¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴² Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁴³ Institute of Astronomy, University of Zielona Góra, Lubuska st. 2, 65-265 Zielona Góra, Poland
⁴⁴ Vintage Lane Observatory, Blenheim, New Zealand
e-mail: whallen@xtra.co.nz
⁴⁵ Perth, Australia
e-mail: gbolt@iinet.net.au
⁴⁶ Molehill Astronomical Observatory, Auckland, New Zealand
e-mail: molehill@ihug.co.nz
⁴⁷ Department of Physics and Astronomy, Texas A&M University, College Station, TX, USA
e-mail: depoy@physics.tamu.edu
⁴⁸ Possum Observatory, Patutahi, New Zealand
e-mail: john_drummond@xtra.co.nz
⁴⁹ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel
e-mail: avishay.gal-yam@weizmann.ac.il
⁵⁰ Hunters Hill Observatory, Canberra, Australia
e-mail: dhi67540@bigpond.net.au
⁵¹ Department of Physics, Technion, Haifa 32000, Israel
⁵² KoreaAstronomy and Space Science Institute, Daejon 305-348, Korea
e-mail: leecu@kasi.re.kr; bgpark@kasi.re.kr
⁵³ Campo Catino Austral Observatory, San Pedro de Atacama, Chile
e-mail: francomallia@campocatinobservatory.org; alain@spaceobs.com
⁵⁴ Kumeu Observatory, Kumeu, New Zealand
e-mail: acrux@orcon.net.nz; guy.thornley@gmail.com
⁵⁵ AUT University, Auckland, New Zealand
e-mail: tim.natusch@aut.ac.nz
⁵⁶ Palomar Observatory, California, USA
e-mail: eran@astro.caltech.edu
⁵⁷ Einstein Fellow  
⁵⁸ Southern Stars Observatory, Faaa, Tahiti, French Polynesia
e-mail: obs930@southernstars-observatory.org
⁵⁹ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁶⁰ Astrophysics Research Institute, Liverpool John Moores University, Liverpool CH41 1LD, UK
⁶¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁶² Deutsches SOFIA Institut, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
⁶³ SOFIA Science Center, NASA Ames Research Center, Mail Stop N211-3, Moffett Field CA 94035, USA
⁶⁴ Jodrell Bank Centre for Astrophysics, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
e-mail: Eamonn.Kerins@manchester.ac.uk
⁶⁵ Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
⁶⁶ Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
⁶⁷ Las Cumbres Observatory Global Telescope network, 6740 Cortona Drive, suite 102, Goleta, CA 93117, USA
⁶⁸ Dept. of Physics, Broida Hall, University of California, Santa Barbara CA 93106-9530, USA
⁶⁹ Università degli Studi di Salerno, Dipartimento di Fisica “E.R. Caianiello”, via Ponte Don Melillo, 84085 Fisciano ( SA), Italy
⁷⁰ Istituto Internazionale per gli Alti Studi Scientifici (IIASS), via G. Pellegrino 19, 84019 Vietri sul Mare ( SA), Italy
⁷¹ INFN, Gruppo Collegato di Salerno, Sezione di Napoli, Italy
⁷² Royal Society University Research Fellow  
⁷³ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁷⁴ Institut d’Astrophysique et de Géophysique, Allée du 6 Août 17, Sart Tilman, Bât. B5c, 4000 Liège, Belgium
⁷⁵ Department of Physics & Astronomy, Aarhus University, Ny Munkegade 120, 8000 Århus C, Denmark
⁷⁶ Armagh Observatory, College Hill, Armagh, BT61 9DG, UK
⁷⁷ Department of Physics, Sharif University of Technology, PO Box 11155–9161, Tehran, Iran
⁷⁸ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁷⁹ School of Astronomy, IPM (Institute for Studies in Theoretical Physics and Mathematics), PO Box 19395-5531, Tehran, Iran
⁸⁰ Dipartimento di Ingegneria, Università del Sannio, Corso Garibaldi 107, 82100 Benevento, Italy
⁸¹ National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012, P.R. China
e-mail: jinan@nao.cas.cn
⁸² School of Physics, University of Western Australia, Perth, WA 6009 Australia

Received: 8 November 2010
Accepted: 17 January 2011

Abstract

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_⊙ < M_host < 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 m_p = 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 θ_E = 0.31 ± 0.03 mas has been accurately measured, but the other (the microlens parallax π_E, 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 < D_L < 7.9   kpc, 1.1   AU < a < 2.7   AU, and 3.8   yr < P < 7.6   yr, respectively.