Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge

Creators: Zang, Weicheng; Shvartzvald, Yossi; Calchi Novati, Sebastiano; Beichman, Charles A.; Carey, Sean; Henderson, Calen B.; Spitzer Team; OGLE Collaboration; LCO Collaboration; µFUN Collaboration; KMTNet Collaboration; MOA Collaboration; MINDSTEP Collaboration

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Abstract

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60±0.03M⊙ star with D_(LS) = 0.53±0.11 kpc, where D_(LS) is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a 0.51^(+0.12)_(−0.10)M⊙ star with D_(LS) = 0.40±0.12 kpc or a 0.38^(+0.13)_(−0.12)M⊙ star with D_(LS) = 0.53±0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurrence in single lens events.

Additional Information

© 2020 The American Astronomical Society. Received 2019 April 24; revised 2020 January 10; accepted 2020 January 17; published 2020 February 27. W.Z., W.T., S.-S.L., and S.M. acknowledge support by the National Science Foundation of China (grants No. 11821303 and 11761131004). This work is based (in part) on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. The OGLE has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. 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 MOA project is supported by JSPS KAKENHI grants No. JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, JP16H06287, and JP17H02871. The research has made use of data obtained at the Danish 1.54 m telescope at ESO's La Silla Observatory. CITEUC is funded by National Funds through FCT—Foundation for Science and Technology (project: UID/Multi/00611/2013) and FEDER—European Regional Development Fund through COMPETE 2020—Operational Programme Competitiveness and Internationalization (project: POCI-01-0145-FEDER-006922). Work by A.G. was supported by AST-1516842 and by JPL grant 1500811. A.G. received support from the European Research Council under the European Unions Seventh Framework Programme (FP 7) ERC grant Agreement No. [321035]. Wei Zhu was supported by the Beatrice and Vincent Tremaine Fellowship at CITA. Work by C.H. was supported by the grant (2017R1A4A1015178) of the National Research Foundation of Korea. Y.T. acknowledges the support of DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (WA 1047/11-1). L.M. acknowledges support from the Italian Minister of Instruction, University and Research (MIUR) through the FFABR 2017 fund.

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