A brown dwarf orbiting an M-dwarf: MOA 2009–BLG–411L
Abstract
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 M_S = 0.05 M_⊙ orbiting a primary M-star of mass M_P = 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.
Additional Information
© 2012 ESO. Received 6 June 2012. Accepted 27 August 2012. Published online 25 October 2012. We are very grateful to the observatories that support our science (Bronberg, Canopus, CTIO, ESO, IRSF, LCOGT, Liverpool, LOAO, MOA, OGLE, Perth, SAAO, Skinakas) via the generous allocation of time that makes this work possible. The operation of Canopus Observatory is in part supported by a financial contribution from David Warren. Allocation of the Holmes grant from the French Agence Nationale de la Recherche has been indispensable to finance observing trips and travel costs for meetings, and is gratefully acknowledged here. D.H. was supported by Czech Science Foundation grant GACR 205/07/0824 and by the Czech Ministry of Education project MSM0021620860. C.H. was supported by the grant 2009-0081561 of National Research Foundation of Korea. T.C.H. was financed for his astronomical research at the Armagh Observatory by the Department for Culture, Arts and Leisure, Northern Ireland, UK and is now supported by the Korea Research Council for Fundamental Science and Technology (KRCF) via the Young Scientist Research Fellowship Program. MOA project was funded by JSPS18253002 and JSPS20340052. T.S. was funded by JSPS20740104. D.R. and J.S. acknowledge support from the Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-Europe. P.F. wishes to thank Noriyuki Matsunaga for discussions about the interplay between adopted distance and derived extinction. The research leading to these results has received funding from the European Community's Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No 229517. A. Gould acknowledges support from NSF AST-1103471. B. S. Gaudi, A. Gould, and R. W. Pogge acknowledge support from NASA grant NNG04GL51G. Work by J. C. Yee is supported by a National Science Foundation Graduate Research Fellowship under Grant No. 2009068160. Work by S. Dong was performed under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. The RoboNet team is supported by the Qatar Foundation through QNRF grant NPRP-09-476-1-78. CUL acknowledges support by Korea Astronomy and Space Science Institute (KASI) grant 2012-1-410-02. This publication makes use of data products from the 2MASS project, as well as the SIMBAD database, Aladin and Vizier catalogue operation tools (CDS Strasbourg, France). The Two Micron All Sky Survey is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work was granted access to the HPC resources of CALMIP under the allocation 2012-[1131].Attached Files
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Additional details
- Eprint ID
- 36431
- Resolver ID
- CaltechAUTHORS:20130116-133725433
- GACR 205/07/0824
- Czech Science Foundation
- MSM0021620860
- Ministry of Education (Czech Republic)
- 2009-0081561
- National Research Foundation of Korea
- Armagh Observatory
- Korea Research Council for Fundamental Science and Technology (KRCF) Young Scientist Research Fellowship Program
- JSPS18253002
- Japan Society for the Promotion of Science (JSPS)
- JSPS20340052
- Japan Society for the Promotion of Science (JSPS)
- JSPS20740104
- Japan Society for the Promotion of Science (JSPS)
- Communauté française de Belgique - Actions de recherche concertées - Académie universitaire Wallonie-Europe
- 229517
- European Community Seventh Framework Programme (FP7/2007-2013)
- AST-1103471
- NSF
- NNG04GL51G
- NASA
- 2009068160
- NSF Graduate Research Fellowship
- NASA Sagan Fellowship
- NPRP-09-476-1-78
- Qatar Foundation QNRF grant
- 2012-1-410-02
- Korea Astronomy and Space Science Institute (KASI)
- NASA
- NSF
- Created
-
2013-01-16Created from EPrint's datestamp field
- Updated
-
2021-11-09Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)