Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge

Zang, Weicheng; Shvartzvald, Yossi; Wang, Tianshu; Udalski, Andrzej; Lee, Chung-Uk; Sumi, Takahiro; Skottfelt, Jesper; Li, Shun-Sheng; Mao, Shude; Zhu, Wei; Yee, Jennifer C.; Calchi Novati, Sebastiano; Beichman, Charles A.; Bryden, Geoffery; Carey, Sean; Gaudi, B. Scott; Henderson, Calen B.; Mróz, Przemek; Skowron, Jan; Poleski, Radoslaw; Szymański, Michał K.; Soszyński, Igor; Pietrukowicz, Paweł; Kozłowski, Szymon; Ulaczyk, Krzysztof; Rybicki, Krzysztof A.; Iwanek, Patryk; Bachelet, Etienne; Christie, Grant; Green, Jonathan; Hennerley, Steve; Maoz, Dan; Natusch, Tim; Pogge, Richard W.; Street, Rachel A.; Tsapras, Yiannis; Albrow, Michael D.; Chung, Sun-Ju; Gould, Andrew; Han, Cheongho; Hwang, Kyu-Ha; Jung, Youn Kil; Ryu, Yoon-Hyun; Shin, In-Gu; Cha, Sang-Mok; Kim, Dong-Jin; Kim, Hyoun-Woo; Kim, Seung-Lee; Lee, Dong-Joo; Lee, Yongseok; Park, Byeong-Gon; Bond, Ian A.; Abe, Fumio; Barry, Richard; Bennett, David P.; Bhattacharya, Aparna; Donachie, Martin; Fukui, Akihiko; Hirao, Yuki; Itow, Yoshitaka; Kondo, Iona; Koshimoto, Naoki; Alex Li, Man Cheung; Matsubara, Yutaka; Muraki, Yasushi; Miyazaki, Shota; Nagakane, Masayuki; Ranc, Clément; Rattenbury, Nicholas J.; Suematsu, Haruno; Sullivan, Denis J.; Suzuki, Daisuke; Tristram, Paul J.; Yonehara, Atsunori; Dominik, Martin; Hundertmark, Markus; Jørgensen, Uffe G.; Rahvar, Sohrab; Sajadian, Sedighe; Snodgrass, Colin; Bozza, Valerio; Burgdorf, Martin J.; Evans, Daniel F.; Jaimes, R. Figuera; Fujii, Yuri I.; Mancini, Luigi; Longa-Peña, Penelope; Helling, Christiane; Peixinho, Nuno; Rabus, Markus; Southworth, John; Unda-Sanzana, Eduardo and Essen, Carolina von (2020). Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge. The Astrophysical Journal, 891(1), article no. 3.

DOI: https://doi.org/10.3847/1538-4357/ab6ff8

Abstract

We report the mass and distance measurements of two single-lens events from the 2017 $\textit {Spitzer}$ 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 $\textit {Spitzer}$ observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60 ± 0.03 M ⊙ 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 ${0.51}_{-0.10}^{+0.12}\,{M}_{\odot }$ star with D LS = 0.40 ± 0.12 kpc or a ${0.38}_{-0.12}^{+0.13}\,{M}_{\odot }$ 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 $\textit {Spitzer}$ finite-source events with the expectations from a Galactic model, we find that the $\textit {Spitzer}$ sample is in agreement with the probability of finite-source effects occurring in single-lens events.

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