Microlensing discovery of a population of very tight, very low mass binary brown dwarfs
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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☉ and 0.034 M☉, 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☉. 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.
Choi , J -Y , Han , C , Udalski , A , Sumi , T , Gaudi , B S , Gould , A , Bennett , D P , Dominik , M , Beaulieu , J -P , Tsapras , Y , Bozza , V , Abe , F , Bond , I A , Botzler , C S , Chote , P , Freeman , M , Fukui , A , Furusawa , K , Itow , Y , Ling , C H , Masuda , K , Matsubara , Y , Miyake , N , Muraki , Y , Ohnishi , K , Rattenbury , N J , Saito , T , Sullivan , D J , Suzuki , K , Sweatman , W L , Suzuki , D , Takino , S , Tristram , P J , Wada , K , Yock , P C M , Szymanski , M K , Kubiak , M , Pietrzynski , G , Soszynski , I , Skowron , J , Kozlowski , S , Poleski , R , Ulaczyk , K , Wyrzykowski , L , Pietrukowicz , P , Almeida , L A , DePoy , D L , Dong , S , Gorbikov , E , Jablonski , F , Henderson , C B , Hwang , K -H , Janczak , J , Jung , Y -K , Kaspi , S , Lee , C -U , Malamud , U , Maoz , D , McGregor , D , Munoz , J A , Park , B -G , Park , H , Pogge , R W , Shvartzvald , Y , Shin , I -G , Yee , J C , Alsubai , K A , Browne , P , Burgdorf , M J , Calchi Novati , S , Dodds , P , Fang , X -S , Finet , F , Glitrup , M , Grundahl , F , Gu , S -H , Hardis , S , Harpsoe , K , Hinse , T C , Hornstrup , A , Hundertmark , M , Jessen-Hansen , J , Jrgensen , U G , Kains , N , Kerins , E , Liebig , C , Lund , M N , Lundkvist , M , Maier , G , Mancini , L , Mathiasen , M , Penny , M T , Rahvar , S , Ricci , D , Scarpetta , G , Skottfelt , J , Snodgrass , C , Southworth , J , Surdej , J , Tregloan-Reed , J , Wambsganss , J , Wertz , O , Zimmer , F , Albrow , M D , Bachelet , E , Batista , V , Brillant , S , Cassan , A , Cole , A A , Coutures , C , Dieters , S , Prester , D D , Donatowicz , J , Fouque , P , Greenhill , J , Kubas , D , Marquette , J -B , Menzies , J W , Sahu , K C , Zub , M , Bramich , D M , Horne , K , Steele , I A & Street , R A 2013 , ' Microlensing discovery of a population of very tight, very low mass binary brown dwarfs ' Astrophysical Journal , vol 768 , no. 2 , 129 . DOI: 10.1088/0004-637X/768/2/129
© 2013. The American Astronomical Society. All rights reserved.
Work by C. Han was supported by the research grant of Chungbuk National University in 2011. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement No. 246678. The MOA experiment was supported by grants JSPS22403003 and JSPS23340064. This work is based in part on data collected by MiNDSTEp with the Danish 1.54 m telescope at the ESO La Silla Observatory, which is operated based on a grant from the Danish Natural Science Foundation (FNU). The MiNDSTEp monitoring campaign is powered by ARTEMiS (Dominik et al. 2008). M.H. acknowledges support by the German Research Foundation (DFG). D.R. (boursier FRIA), F.F. (boursier ARC), and J. Surdej acknowledge support from the Communauté française de Belgique—Actions de recherche concertées—Académie universitaire Wallonie-Europe. K.A., D.M.B., M.D., K.H., M.H., C.L., C.S., R.A.S., and Y.T. are thankful to the Qatar National Research Fund (QNRF), member of the Qatar Foundation, for support by grant NPRP 09-476-1-078. C.S. has received funding from FP7/2007-2013 under grant agreement No. 268421. K.H. is supported by a Royal Society Leverhulme Trust Senior Research Fellowship. A.G. and B.S.G. acknowledge support from NSF AST-1103471. B.S.G., A.G., and R.W.P. acknowledge support from NASA grant NNX12AB99G. Work by J.C.Y. is supported by a National Science Foundation Graduate Research Fellowship under grant No. 2009068160. S.D.'s research was performed under contract with the California Institute of Technology funded by NASA through the Sagan Fellowship Program. T.S. was supported by the grant JSPS23340044. Y.M. acknowledges support from JSPS grants JSPS23540339 and JSPS19340058. T.C.H. and C.U.L. acknowledge the support of KASI grant 2012-1-410-02 and KRCF.
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