November
2012
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2012A&A...547A..55B
Authors
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Bachelet, E.
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Fouqué, P.
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Han, C.
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Gould, A.
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Albrow, M. D.
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Beaulieu, J. -P.
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Bertin, E.
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Bond, I. A.
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Christie, G. W.
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Heyrovský, D.
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Horne, K.
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Jørgensen, U. G.
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Maoz, D.
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Mathiasen, M.
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Matsunaga, N.
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McCormick, J.
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Menzies, J.
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Nataf, D.
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Natusch, T.
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Oi, N.
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Renon, N.
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Tsapras, Y.
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Udalski, A.
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Yee, J. C.
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Batista, V.
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Bennett, D. P.
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Brillant, S.
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Caldwell, J. A. R.
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Cassan, A.
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Cole, A.
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Cook, K. H.
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Coutures, C.
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Dieters, S.
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Dominik, M.
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Dominis Prester, D.
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Donatowicz, J.
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Greenhill, J.
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Kains, N.
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Kane, S. R.
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Marquette, J. -B.
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Martin, R.
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Pollard, K. R.
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Sahu, K. C.
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Street, R. A.
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Wambsganss, J.
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Williams, A.
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Zub, M.
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PLANET Collaboration
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Bos, M.
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Dong, Subo
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Drummond, J.
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Gaudi, B. S.
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Graff, D.
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Janczak, J.
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Kaspi, S.
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Kozłowski, S.
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Lee, C. -U.
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Monard, L. A. G.
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Muñoz, J. A.
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Park, B. -G.
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Pogge, R. W.
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Polishook, D.
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Shporer, A.
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Fun Collaboration
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Abe, F.
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Botzler, C. S.
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Fukui, A.
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Furusawa, K.
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Hearnshaw, J. B.
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Itow, Y.
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Korpela, A. V.
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Ling, C. H.
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Masuda, K.
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Matsubara, Y.
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Miyake, N.
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Muraki, Y.
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Ohnishi, K.
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Rattenbury, N. J.
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Saito, To.
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Sullivan, D.
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Sumi, T.
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Suzuki, D.
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Sweatman, W. L.
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Tristram, P. J.
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Wada, K.
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MOA Collaboration
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Allan, A.
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Bode, M. F.
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Bramich, D. M.
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Clay, N.
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Fraser, S. N.
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Hawkins, E.
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Kerins, E.
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Lister, T. A.
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Mottram, C. J.
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Saunders, E. S.
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Snodgrass, C.
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Steele, I. A.
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Wheatley, P. J.
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ROBONET-II Collaboration
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Bozza, V.
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Browne, P.
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Burgdorf, M. J.
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Calchi Novati, S.
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Dreizler, S.
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Finet, F.
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Glitrup, M.
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Grundahl, F.
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HarpsøE, K.
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Hessman, F. V.
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Hinse, T. C.
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Hundertmark, M.
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Liebig, C.
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Maier, G.
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Mancini, L.
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Rahvar, S.
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Ricci, D.
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Scarpetta, G.
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Skottfelt, J.
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Southworth, J.
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Surdej, J.
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Zimmer, F.
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Mindstep Consortium
Abstract
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Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.
Aims: MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.
Methods: Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components.
Results: We find that the source star is a giant G star with radius 9 R⊙. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s-1. We find that the lens is composed of a brown dwarf secondary of mass MS = 0.05 M⊙ orbiting a primary M-star of mass MP = 0.18 M⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries.
Conclusions: As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf.
Appendix is available in electronic form at
http://www.aanda.org
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