Characterizing low-mass binaries from observation of long-timescale caustic-crossing gravitational microlensing events

Shin, I.-G.; Han, C.; Choi, J.-Y.; Udalski, A.; Sumi, T.; Gould, A.; Bozza, V.; Dominik, M.; Fouqué, P.; Horne, K.; Szymański, M. K.; Kubiak, M.; Soszyński, I.; Pietrzyński, G.; Poleski, R.; Ulaczyk, K.; Pietrukowicz, P.; Kozłowski, S.; Skowron, J.; Wyrzykowski, Ł.; Abe, F.; Bennett, D. P.; Bond, I. A.; Botzler, C. S.; Chote, P.; Freeman, M.; Fukui, A.; Furusawa, K.; Itow, Y.; Kobara, S.; Ling, C. H.; Masuda, K.; Matsubara, Y.; Miyake, N.; Muraki, Y.; Ohmori, K.; Ohnishi, K.; Rattenbury, N. J.; Saito, To.; Sullivan, D. J.; Suzuki, D.; Suzuki, K.; Sweatman, W. L.; Takino, S.; Tristram, P. J.; Wada, K.; Yock, P. C. M.; Bramich, D. M.; Snodgrass, C.; Steele, I. A.; Street, R. A.; Tsapras, Y.; Alsubai, K. A.; Browne, P.; Burgdorf, M. J.; Calchi Novati, S.; Dodds, P.; Dreizler, S.; Fang, X.-S.; Grundahl, F.; Gu, C.-H.; Hardis, S.; Harpsøe, K.; Hinse, T. C.; Hornstrup, A.; Hundertmark, M.; Jessen-Hansen, J.; Jørgensen, U. G.; Kains, N.; Kerins, E.; Liebig, C.; Lund, M.; Lunkkvist, M.; Mancini, L.; Mathiasen, M.; Penny, M. T.; Rahvar, S.; Ricci, D.; Scarpetta, G.; Skottfelt, J.; Southworth, J.; Surdej, J.; Tregloan-Reed, J.; Wambsganss, J.; Wertz, O.; Almeida, L. A.; Batista, V.; Christie, G.; DePoy, D. L.; Dong, Subo; Gaudi, B. S.; Henderson, C.; Jablonski, F.; Lee, C.-U.; McCormick, J.; McGregor, D.; Moorhouse, D.; Natusch, T.; Ngan, H.; Park, S.-Y.; Pogge, R. W.; Tan, T.-G.; Thornley, G.; Yee, J. C.; Albrow, M. D.; Bachelet, E.; Beaulieu, J.-P.; Brillant, S.; Cassan, A.; Cole, A. A.; Corrales, E.; Coutures, C.; Dieters, S.; Dominis Prester, D.; Donatowicz, J.; Greenhill, J.; Kubas, D.; Marquette, J.-B.; Menzies, J. W.; Sahu, K. C. and Zub, M. (2012). Characterizing low-mass binaries from observation of long-timescale caustic-crossing gravitational microlensing events. Astrophysical Journal, 755(2), article no. 91.

DOI: https://doi.org/10.1088/0004-637X/755/2/91

Abstract

Despite the 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 two 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. The measured masses of the binary components are 0.43 M and 0.39 M for MOA-2011-BLG-090 and 0.57 M and 0.17 M 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. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. 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.

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