OGLE-2017-BLG-0329L: A Microlensing Binary Characterized with Dramatically Enhanced Precision Using Data from Space-based Observations

MiNDSTEp Collaboration, KMTNet Collaboration, OGLE Collaboration, Spitzer Team, C. Han (Lead / Corresponding author), S. Calchi Novati, A. Udalski, C. -U. Lee, A. Gould, V. Bozza, P. Mróz, P. Pietrukowicz, J. Skowron, M. K. Szymański, R. Poleski, I. Soszyński, S. Kozłowski, K. Ulaczyk, M. Pawlak, K. RybickiP. Iwanek, M. D. Albrow, S. -J. Chung, K. -H. Hwang, Y. K. Jung, Y. -H. Ryu, I. -G. Shin, Y. Shvartzvald, J. C. Yee, W. Zang, W. Zhu, S. -M. Cha, D. -J. Kim, H. -W. Kim, S. -L. Kim, D. -J. Lee, Y. Lee, B. -G. Park, R. W. Pogge, W. -T. Kim, C. Beichman, G. Bryden, S. Carey, B. S. Gaudi, C. B. Henderson, M. Dominik, C. Helling, M. Hundertmark, U. G. Jørgensen, P. Longa-Peña, S. Lowry, S. Sajadian, M. J. Burgdorf, J. Campbell-White, Simona Ciceri, D. F. Evans, L. K. Haikala, T. C. Hinse, S. Rahvar, M. Rabus, C. Snodgrass

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Mass measurements of gravitational microlenses require one to determine the microlens parallax πE, but precise πE measurement, in many cases, is hampered due to the subtlety of the microlens-parallax signal combined with the difficulty of distinguishing the signal from those induced by other higher-order effects. In this work, we present the analysis of the binary-lens event OGLE-2017-BLG-0329, for which πE is measured with a dramatically improved precision using additional data from space-based Spitzer observations. We find that while the parallax model based on the ground-based data cannot be distinguished from a zero-πE model at the 2σ level, the addition of the Spitzer data enables us to identify two classes of solutions, each composed of a pair of solutions according to the wellknown ecliptic degeneracy. It is found that the space-based data reduce the measurement uncertainties of the north and east components of the microlens-parallax vector pE by factors ∼18 and ∼4, respectively. With the measured microlens parallax combined with the angular Einstein radius measured from the resolved caustic crossings, we find that the lens is composed of a binary with component masses of either (M1, M2) ∼ (1.1, 0.8) Me or ∼(0.4, 0.3) Me according to the two solution classes. The first solution is significantly favored but the second cannot be securely ruled out based on the microlensing data alone. However, the degeneracy can be resolved from adaptive optics observations taken ∼10 years after the event.
Original languageEnglish
Article number82
Pages (from-to)1-10
Number of pages10
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 25 May 2018


  • binaries: general
  • gravitational lensing: micro


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