Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

Creators: Zang, Weicheng; Dong, Subo; Gould, Andrew; Calchi Novati, Sebastiano; Chen, Ping; Yang, Hongjing; Li, Shun-Sheng; Mao, Shude; Alton, K. B.; Brimacombe, J.; Carey, Sean; Christie, G. W.; Delplancke-Ströbele, F.; Feliz, Dax L.; Gaudi, B. Scott; Green, J.; Hu, Shaoming; Jayasinghe, T.; Koff, R. A.; Kurtenkov, A.; Mérand, A.; Minev, Milen; Mutel, Robert; Natusch, T.; Roth, Tyler; Shvartzvald, Yossi; Sun, Fengwu; Vanmunster, T.; Zhu, Wei

Abstract

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector π_E using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this π_E determination with the angular Einstein radius θ_E measured by VLTI-GRAVITY observations, we find that the lens is a star with mass M_L = 0.495±0.063 M⊙ at a distance D_L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is Μ_(rel,hel) = 26.55±0.36 mas yr⁻¹, so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

Additional Information

© 2020 The American Astronomical Society. Received 2019 November 29; revised 2020 May 18; accepted 2020 May 18; published 2020 July 16. We thank Tianshu Wang, Jennifer Yee, Akihiko Fukui, and Naoki Koshimoto for fruitful discussions. We are grateful to Robin Leadbeater and Paolo Berardi for making their spectroscopic observations available to us during the observing campaign. S.D. and P.C. are supported by the National Key R&D Program of China No. 2019YFA0405100 and Projects 11573003 supported by the National Science Foundation of China (NSFC). W.Z., H.Y., S.-S.L., and S.M. acknowledge support by the National Science Foundation of China (grant No. 11821303 and 11761131004). Work by AG 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]. 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. Work by S.M.Hu. was supported by the Natural Science Foundation of Shandong province (No. JQ201702), and the Young Scholars Program of Shandong University (No. 20820162003). W.Z. was supported by the Beatrice and Vincent Tremaine Fellowship at CITA.

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