A brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L

E. Bachelet, P. Fouqué, C. Han, A. Gould, M. D. Albrow, J. P. Beaulieu, E. Bertin, I. A. Bond, G. W. Christie, D. Heyrovský, K. Horne, U. G. Jørgensen, D. Maoz, M. Mathiasen, N. Matsunaga, J. McCormick, J. Menzies, D. Nataf, T. Natusch, N. OiN. Renon, Y. Tsapras, A. Udalski, J. C. Yee, V. Batista, D. P. Bennett, S. Brillant, J. A.R. Caldwell, A. Cassan, A. Cole, K. H. Cook, C. Coutures, S. Dieters, M. Dominik, D. Dominis Prester, J. Donatowicz, J. Greenhill, N. Kains, S. R. Kane, J. B. Marquette, R. Martin, K. R. Pollard, K. C. Sahu, R. A. Street, J. Wambsganss, A. Williams, M. Zub, M. Bos, Subo Dong, J. Drummond, B. S. Gaudi, D. Graff, J. Janczak, S. Kaspi, S. Kozłowski, C. U. Lee, L. A.G. Monard, J. A. Muñoz, B. G. Park, R. W. Pogge, D. Polishook, A. Shporer, F. Abe, C. S. Botzler, A. Fukui, K. Furusawa, J. B. Hearnshaw, Y. Itow, A. V. Korpela, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, K. Ohnishi, N. J. Rattenbury, To Saito, D. Sullivan, T. Sumi, D. Suzuki, W. L. Sweatman, P. J. Tristram, K. Wada, A. Allan, M. F. Bode, D. M. Bramich, N. Clay, S. N. Fraser, E. Hawkins, E. Kerins, T. A. Lister, C. J. Mottram, E. S. Saunders, C. Snodgrass, I. A. Steele, P. J. Wheatley, V. Bozza, P. Browne, M. J. Burgdorf, S. Calchi Novati, S. Dreizler, F. Finet, M. Glitrup, F. Grundahl, K. Harpsøe, F. V. Hessman, T. C. Hinse, M. Hundertmark, C. Liebig, G. Maier, L. Mancini, S. Rahvar, D. Ricci, G. Scarpetta, J. Skottfelt, J. Southworth, J. Surdej, F. Zimmer

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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 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.

Original languageEnglish
Article numberA55
JournalAstronomy and Astrophysics
Volume547
DOIs
Publication statusPublished - 30 Oct 2012

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Keywords

  • Binaries: general
  • Gravitational lensing: micro
  • Stars: individual: MOA 2009-BLG-411L

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bachelet, E., Fouqué, P., Han, C., Gould, A., Albrow, M. D., Beaulieu, J. P., Bertin, E., Bond, I. A., Christie, G. W., Heyrovský, D., Horne, K., Jørgensen, U. G., Maoz, D., Mathiasen, M., Matsunaga, N., McCormick, J., Menzies, J., Nataf, D., Natusch, T., ... Zimmer, F. (2012). A brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L. Astronomy and Astrophysics, 547, [A55]. https://doi.org/10.1051/0004-6361/201219765