Ground-based Parallax Confirmed by Spitzer: Binary Microlensing Event MOA-2015-BLG-020

Creators: Wang, Tianshu; Beichman, C.; Calchi Novati, S.; Carey, S.; MOA Collaboration; OGLE Collaboration; Spitzer Team; KMTNet Collaboration; ROBONET Collaboration

Abstract

We present the analysis of the binary gravitational microlensing event MOA-2015-BLG-020. The event has a fairly long timescale (~63 days) and thus the light curve deviates significantly from the lensing model that is based on the rectilinear lens-source relative motion. This enables us to measure the microlensing parallax through the annual parallax effect. The microlensing parallax parameters constrained by the ground-based data are confirmed by the Spitzer observations through the satellite parallax method. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined. It is found that the binary lens is composed of two dwarf stars with masses M_1 = 0.606 ± 0.028 M⊙ and M_2 = 0.125 ± 0.006 M⊙ in the Galactic disk. Assuming that the source star is at the same distance as the bulge red clump stars, we find the lens is at a distance D_L = 2.44 ± 0.10 kpc. We also provide a summary and short discussion of all of the published microlensing events in which the annual parallax effect is confirmed by other independent observations.

Additional Information

© 2017 The American Astronomical Society. Received 2017 June 16; revised 2017 July 8; accepted 2017 July 14; published 2017 August 18. This work has been supported in part by the National Natural Science Foundation of China (NSFC) grants 11333003 and 11390372 (S.M.). This research uses data obtained through the Telescope Access Program (TAP), which has been funded by the Strategic Priority Research Program "The Emergence of Cosmological Structures" (grant No. XDB09000000), National Astronomical Observatories, Chinese Academy of Sciences, and the Special Fund for Astronomy from the Ministry of Finance. Work by W.Z., Y.K.J., I.G.S., and A.G. was supported by AST-1516842 from the US NSF and JPL grant 1500811. Work by J.C.Y. was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. The OGLE Team thanks Drs. G. Pietrzyński and Ł. Wyrzykowski for their contribution to the collection of the OGLE photometric data over the past years. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. Work by C.H. was supported by the grant (2017R1A4A1015178) of the National Research Foundation of Korea. This work makes use of observations from the LCO network, which includes three SUPAscopes owned by the University of St Andrews. The RoboNet programme was an LCO Key Project using time allocations from the University of St Andrews, LCOGT, and the University of Heidelberg together with time on the Liverpool Telescope through the Science and Technology Facilities Council (STFC), UK. This research has made use of the LCO Archive, which was operated by the California Institute of Technology, under contract with the Las Cumbres Observatory. The MOA project is supported by JSPS KAKENHI grant Nos. JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, and JP16H06287. Software: corner.py (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), VBBinaryLensing (Bozza 2010).

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Submitted - 1707.07737.pdf

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