1204.2869 (I. -G. Shin et al.)

Characterizing Low-Mass Binaries From Observation of Long Time-scale Caustic-crossing Gravitational Microlensing Events    [PDF]

I. -G. Shin, C. Han, J. -Y. Choi, A. Udalski, T. Sumi, A. Gould, V. Bozza, M. Dominik, P. Fouqué, K. Horne, M. \, K. Szymański, M. Kubiak, I. Soszyński, G. Pietrzyński, R. Poleski, K. Ulaczyk, P. Pietrukowicz, S. Kozłowski, J. Skowron, Ł. Wyrzykowski, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler, P. Chote, M. Freeman, A. Fukui, K. Furusawa, Y. Itow, S. Kobara, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, K. Ohmori, K. Ohnishi, N. J. Rattenbury, To. Saito, D. J. Sullivan, D. Suzuki, K. Suzuki, W. L. Sweatman, S. Takino, P. J. Tristram, K. Wada, P. C. M. Yock, D. M. Bramich, C. Snodgrass, I. A. Steele, R. A. Street, Y. Tsapras, K. A. Alsubai, P. Browne, M. J. Burgdorf, S. Calchi Novati, P. Dodds, S. Dreizler, X. -S. Fang, F. Grundahl, C. -H. Gu, S. Hardis, K. Harpsøe, T. C. Hinse, A. Hornstrup, M. Hundertmark, J. Jessen-Hansen, U. G. Jørgensen, N. Kains, E. Kerins, C. Liebig, M. Lund, M. Lunkkvist, L. Mancini, M. Mathiasen, M. T. Penny, S. Rahvar, D. Ricci, G. Scarpetta, J. Skottfelt, J. Southworth, J. Surdej, J. Tregloan-Reed, J. Wambsganss, O. Wertz, L. A. Almeida, V. Batista, G. Christie, D. L. DePoy, Subo Dong, B. S. Gaudi, C. Henderson, F. Jablonski, C. -U. Lee, J. McCormick, D. McGregor, D. Moorhouse, T. Natusch, H. Ngan, S. -Y. Park, R. W. Pogge, T. -G. Tan, G. Thornley, J. C. Yee, M. D. Albrow, E. Bachelet, J. -P. Beaulieu, S. Brillant, A. Cassan, A. A. Cole, E. Corrales, C. Coutures, S. Dieters, D. Dominis Prester, J. Donatowicz, J. Greenhill, D. Kubas, J. -B. Marquette, J. W. Menzies, K. C. Sahu, M. Zub

Despite astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of 2 binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax from analyses of the well-resolved caustic-crossing parts of the light curve and the long-term deviation induced by the orbital motion of the Earth around the Sun, respectively. The measured masses of the binary components are 0.43 $M_{\odot}$ and 0.39 $M_{\odot}$ for MOA-2011-BLG-090 and 0.57 $M_{\odot}$ and 0.17 $M_{\odot}$ for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future.

View original: http://arxiv.org/abs/1204.2869