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

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Bachelet, E and Fouque, P and Han, C and Gould, A and Albrow, MD and Beaulieu, J-P and Bertin, E and Bond, IA and Christie, GW and Heyrovski, D and Horne, K and Jorgensen, UG and Maoz, D and Mathiasen, M and Matsunaga, N and McCormick, J and Menzies, J and Nataf, D and Natusch, T and Oi, N and Renon, N and Tsapras, Y and Udalski, A and Yee, JC and Batista, V and Bennett, DP and Brillant, S and Caldwell, JAR and Cassan, A and Cole, A and Cook, KH and Coutures, C and Dieters, S and Dominik, M and Dominis Prester, D and Donatowicz, J and Greenhill, J and Kains, N and Kane, SR and Marquette, J-B and Martin, R and Pollard, KR and Sahu, KC and Street, RA and Wambsganss, J and Williams, A and Zub, M and Bos, M and Dong, S and Drummond, J and Gaudi, BS and Graff, D and Janczak, J and Kaspi, S and Kozlowski, S and Lee, C-U and Monard, LAG and Munoz, JA and Park, B-G and Pogge, RW and Polishook, D and Shporer, A and Abe, F and Botzler, CS and Fukui, A and Furusawa, K and Hearnshaw, JB and Itow, Y and Korpela, AV and Ling, CH and Masuda, K and Matsubara, Y and Miyake, N and Muraki, Y and Ohnishi, K and Rattenbury, NJ and Saito, T and Sullivan, D and Sumi, T and Suzuki, D and Sweatman, WL and Tristram, PJ and Wada, K and Allan, A and Bode, MF and Bramich, DM and Clay, N and Fraser, SN and Hawkins, E and Kerins, E and Lister, TA and Mottram, CJ and Saunders, ES and Snodgrass, C and Steele, IA and Wheatley, PJ and Bozza, V and Browne, P and Burgdorf, MJ and Calchi Novati, S and Dreizler, S and Finet, F and Glitrup, M and Grundahl, F and Harpsoe, K and Hessman, FV and Hinse, TC and Hundertmark, M and Liebig, C and Maier, G and Mancini, L and Rahvar, S and Ricci, D and Scarpetta, G and Skottfelt, J and Southworth, J and Surdej, J and Zimmer, F, A brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L, Astronomy and Astrophysics, 547 Article A55. ISSN 0004-6361 (2012) [Refereed Article]


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Copyright 2012 ESO

DOI: doi:10.1051/0004-6361/201219765

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.

Item Details

Item Type:Refereed Article
Keywords:binaries: general / gravitational lensing: micro / stars: individual: MOA 2009-BLG-411L
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Stellar Astronomy and Planetary Systems
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Cole, A (Associate Professor Andrew Cole)
Author:Greenhill, J (Dr John Greenhill)
ID Code:82637
Year Published:2012
Web of Science® Times Cited:12
Deposited By:Mathematics and Physics
Deposited On:2013-02-08
Last Modified:2017-11-06
Downloads:274 View Download Statistics

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