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

E. Bachelet, P. Fouque, C. Han, A. Gould, M. D. Albrow, J. -P. Beaulieu, E. Bertin, I. A. Bond, G. W. Christie, D. Heyrovsky, K. Horne, U. G. Jorgensen, 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. Kozlowski, C. -U. Lee, L. A. G. Monard, J. A. Munoz, 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. Harpsoe, 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

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

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, alpha) 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-circle dot. 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-circle dot orbiting a primary M-star of mass M-P = 0.18 M-circle dot. 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
Number of pages12
JournalAstronomy & Astrophysics
Volume547
DOIs
Publication statusPublished - Nov 2012

Keywords

  • binaries: general
  • gravitational lensing: micro
  • stars: individual: MOA 2009-BLG-411L
  • MAGNIFICATION MICROLENSING EVENTS
  • SURFACE BRIGHTNESS RELATIONS
  • DIFFERENCE IMAGE-ANALYSIS
  • CLUMP ABSOLUTE MAGNITUDE
  • GALACTIC BULGE FIELDS
  • INTERSTELLAR EXTINCTION
  • BINARY INTERPRETATIONS
  • CENTRAL PERTURBATIONS
  • PLANETARY SYSTEMS
  • MASS PLANET

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