Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
Feliz, Dax L.; Zang, Weicheng; Gould, Andrew; Shvartzvald, Yossi; Yang, Hongjing; Sun, Fengwu; Dong, Subo; Brimacombe, J.; Gaudi, B. Scott; Minev, Milen; Alton, K. B.; Carey, Sean; Vanmunster, T.; Zhu, Wei; Mao, Shude; Calchi Novati, Sebastiano; Mérand, A.; Hu, Shaoming; Jayasinghe, T.; Chen, Ping; Christie, G. W.; Kurtenkov, A.; Natusch, T.; Delplancke-Ströbele, F.; Koff, R. A.; Li, Shun-Sheng; Green, J.; Mutel, Robert; Roth, Tyler
China, Germany, United States, Chile, Australia, New Zealand, Bulgaria, Israel, Belgium, Canada
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 ${{\boldsymbol{\pi }}}_{{\rm{E}}}$ 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 ${{\boldsymbol{\pi }}}_{{\rm{E}}}$ determination with the angular Einstein radius ${\theta }_{{\rm{E}}}$ measured by VLTI-GRAVITY observations, we find that the lens is a star with mass ${M}_{{\rm{L}}}=0.495\pm 0.063\,{M}_{\odot }$ at a distance DL = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is ${\mu }_{\mathrm{rel},\mathrm{hel}}=26.55\pm 0.36\,\mathrm{mas}\,{\mathrm{yr}}^{-1}$ , 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.