OGLE-2015-BLG-0479LA,B: binary gravitational microlens characterized by simultaneous ground-based and space-based observation

C. Han, A. Udalski, A. Gould, Wei Zhu, R. A. Street, J. C. Yee, C. Beichman, C. Bryden, S. Calchi Novati, S. Carey, M. Fausnaugh, B. S. Gaudi, Calen B. Henderson, Y. Shvartzvald, B. Wibking, M. K. Szymański, I. Soszyński, J. Skowron, P. Mróz, R. PoleskiP. Pietrukowicz, S. Kozłowski, K. Ulaczyk, Ł. Wyrzykowski, M. Pawlak, Y. Tsapras, M. Hundertmark, E. Bachelet, M. Dominik, D. M. Bramich, A. Cassan, R. Figuera Jaimes, K. Horne, C. Ranc, R. Schmidt, C. Snodgrass, J. Wambsganss, I. A. Steele, J. Menzies, S. Mao, V. Bozza, U. G. Jørgensen, K. A. Alsubai, S. Ciceri, G. D'Ago, T. Haugbølle, F. V. Hessman, T. C. Hinse, D. Juncher, H. Korhonen, L. Mancini, A. Popovas, M. Rabus, S. Rahvar, G. Scarpetta, J. Skottfelt, J. Southworth, D. Starkey, J. Surdej, O. Wertz, M. Zarucki, R. W. Pogge, D. L. DePoy

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14 Citations (Scopus)


We present a combined analysis of the observations of the gravitational microlensing event OGLE-2015-BLG-0479 taken both from the ground and by the Spitzer Space Telescope. The light curves seen from the ground and from space exhibit a time offset of ~13 days between the caustic spikes, indicating that the relative lens-source positions seen from the two places are displaced by parallax effects. From modeling the light curves, we measure the space-based microlens parallax. Combined with the angular Einstein radius measured by analyzing the caustic crossings, we determine the mass and distance of the lens. We find that the lens is a binary composed of two G-type stars with masses of ~1.0 M ⊙ and ~0.9 M ⊙ located at a distance of ~3 kpc. In addition, we are able to constrain the complete orbital parameters of the lens thanks to the precise measurement of the microlens parallax derived from the joint analysis. In contrast to the binary event OGLE-2014-BLG-1050, which was also observed by Spitzer, we find that the interpretation of OGLE-2015-BLG-0479 does not suffer from the degeneracy between (±, ±) and (±, mnplus) solutions, confirming that the four-fold parallax degeneracy in single-lens events collapses into the two-fold degeneracy for the general case of binary-lens events. The location of the blend in the color–magnitude diagram is consistent with the lens properties, suggesting that the blend is the lens itself. The blend is bright enough for spectroscopy and thus this possibility can be checked from future follow-up observations.
Original languageEnglish
Article number53
Number of pages9
JournalAstrophysical Journal
Issue number1
Early online date29 Aug 2016
Publication statusPublished - 1 Sept 2016


  • Binaries: general
  • Gravitational lensing: micro


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