[en] Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M [SUB]⊙[/SUB] and 0.034 M [SUB]⊙[/SUB], and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of ~0.02 M [SUB]⊙[/SUB]. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Choi, J.-Y.; Department of Physics, Institute for Astrophysics, Chungbuk National University, Cheongju 371-763, Republic of Korea
Han, C.; Department of Physics, Institute for Astrophysics, Chungbuk National University, Cheongju 371-763, Republic of Korea ; The μFUN Collaboration. ; Corresponding author.
Udalski, A.; Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland ; The OGLE Collaboration.
Sumi, T.; Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan ; The MOA Collaboration.
Gaudi, B. S.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA ; The μFUN Collaboration.
Gould, A.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA ; The μFUN Collaboration.
Bennett, D. P.; Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556-5670, USA ; The MOA Collaboration.
Dominik, M.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK ; The MiNDSTEp Consortium. ; The RoboNet Collaboration. ; Royal Society University Research Fellow.
Beaulieu, J.-P.; Institut dAstrophysique de Paris, UMR7095 CNRS-Université Pierre & Marie Curie, 98 bis boulevard Arago, F-75014 Paris, France ; The PLANET Collaboration.
Tsapras, Y.; Las Cumbres Observatory Global Telescope Network, 6740B Cortona Drive, Goleta, CA 93117, USA ; School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK ; The RoboNet Collaboration.
Bozza, V.; INFN, Sezione di Napoli, I-80126 Napoli, Italy ; Dipartimento di Fisica E.R. Caianiello¡, Università di Salerno, Via Ponte Don Melillo, I-84084 Fisciano (SA), Italy ; The MiNDSTEp Consortium.
Yee, J. C.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
The μFUN Collaboration
Alsubai, K. A.; Qatar Foundation, P.O. Box 5825, Doha, Qatar
Calchi Novati, S.; Istituto Internazionale per gli Alti Studi Scientifici (IIASS), I-84019 Vietri Sul Mare (SA), Italy
Dodds, P.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
Fang, X.-S.; National Astronomical Observatories/Yunnan Observatory, Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China
Finet, F.; Institut dAstrophysique et de Géophysique, Allé du 6 Août 17, Sart Tilman, Bât. B5c, B-4000 Liège, Belgium
Glitrup, M.; Stellar Astrophysics Center (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark
Grundahl, F.; Stellar Astrophysics Center (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark
Gu, S.-H.; National Astronomical Observatories/Yunnan Observatory, Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China
Scarpetta, G.; INFN, Sezione di Napoli, I-80126 Napoli, Italy ; Istituto Internazionale per gli Alti Studi Scientifici (IIASS), I-84019 Vietri Sul Mare (SA), Italy
Hardis, S.; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark
Southworth, J.; Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Harpsøe, K.; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark ; Centre for Star and Planet Formation, Geological Museum, ster Voldgade 5, DK-1350 Copenhagen, Denmark
Hinse, T. C.; Korea Astronomy and Space Science Institute, Daejeon 305-348, Republic of Korea ; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark
Hornstrup, A.; Institut for Rumforskning og-teknologi, Danmarks Tekniske Universitet, Juliane Maries Vej 30, DK-2100 København, Denmark
Hundertmark, M.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK ; Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany
Jessen-Hansen, J.; Stellar Astrophysics Center (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark ; Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain
Jrgensen, U. G.; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark ; Centre for Star and Planet Formation, Geological Museum, ster Voldgade 5, DK-1350 Copenhagen, Denmark
Kains, N.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK ; ESO Headquarters, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
Kerins, E.; Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
Skottfelt, J.; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark
Liebig, C.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK ; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
Lund, M. N.; Stellar Astrophysics Center (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark
Surdej, Jean ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Lundkvist, M.; Stellar Astrophysics Center (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark
Maier, G.; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
Mancini, L.; Dipartimento di Fisica E.R. Caianiello¡, Università di Salerno, Via Ponte Don Melillo, I-84084 Fisciano (SA), Italy ; Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
Mathiasen, M.; Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-2100 Copenhagen, Denmark
Penny, M. T.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA ; Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
Rahvar, S.; Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Iran ; Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L2Y5, Canada
Ricci, Davide ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Snodgrass, C.; Max Planck Institute for Solar System Research, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau, Germany ; European Southern Observatory (ESO), Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
Tregloan-Reed, J.; Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
Wambsganss, J.; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
Wertz, Olivier ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Zimmer, F.; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
MiNDSTEp Consortium, The
Albrow, M. D.; Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
Bachelet, E.; IRAP, Université de Toulouse, CNRS, 14 Avenue Edouard Belin, F-31400 Toulouse, France
Steele, I. A.; Astrophysics Research Institute, Liverpool John Moores University, Liverpool CH41 1LD, UK
Batista, V.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
Abe, F.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Brillant, S.; European Southern Observatory (ESO), Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
Cassan, A.; UPMC-CNRS, UMR 7095, Institut dAstrophysique de Paris, 98bis boulevard Arago, F-75014 Paris, France
Cole, A. A.; School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia
Coutures, C.; UPMC-CNRS, UMR 7095, Institut dAstrophysique de Paris, 98bis boulevard Arago, F-75014 Paris, France
Dieters, S.; School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia
Dominis Prester, D.; Department of Physics, University of Rijeka, Omladinska 14, 51000 Rijeka, Croatia
Donatowicz, J.; Department of Computing, Technical University of Vienna, Wiedner Hauptstrasse, A-1040 Vienna, Austria
Fouqué, P.; IRAP, Université de Toulouse, CNRS, 14 Avenue Edouard Belin, F-31400 Toulouse, France
Street, R. A.; Las Cumbres Observatory Global Telescope Network, 6740B Cortona Drive, Goleta, CA 93117, USA
Greenhill, J.; School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia
Kubas, D.; European Southern Observatory (ESO), Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile ; UPMC-CNRS, UMR 7095, Institut dAstrophysique de Paris, 98bis boulevard Arago, F-75014 Paris, France
Bond, I. A.; Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland 0745, New Zealand
Marquette, J.-B.; UPMC-CNRS, UMR 7095, Institut dAstrophysique de Paris, 98bis boulevard Arago, F-75014 Paris, France
Menzies, J. W.; South African Astronomical Observatory, P.O. Box 9, Observatory 7925, South Africa
Sahu, K. C.; Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
Zub, M.; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
The PLANET Collaboration
Bramich, D. M.; European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
Horne, K.; SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
The RoboNet Collaboration; )
Botzler, C. S.; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand
Chote, P.; School of Chemical and Physical Sciences, Victoria University, Wellington 6140, New Zealand
Freeman, M.; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand
Fukui, A.; Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232, Japan
Furusawa, K.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Itow, Y.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Ling, C. H.; Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland 0745, New Zealand
Skowron, J.; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
Masuda, K.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Matsubara, Y.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Miyake, N.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Muraki, Y.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Ohnishi, K.; Nagano National College of Technology, Nagano 381-8550, Japan
Rattenbury, N. J.; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand
Saito, To; Tokyo Metropolitan College of Aeronautics, Tokyo 116-8523, Japan
Sullivan, D. J.; School of Chemical and Physical Sciences, Victoria University, Wellington 6140, New Zealand
Suzuki, K.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Sweatman, W. L.; Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland 0745, New Zealand
Suzuki, D.; Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan
Takino, S.; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
Tristram, P. J.; Mt. John University Observatory, P.O. Box 56, Lake Tekapo 8770, New Zealand
Wada, K.; Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan
Yock, P. C. M.; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand
The MOA Collaboration
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