Asteroidscomets

Spitzer Microlensing of MOA-2016-BLG-231L: A Counter-rotating Brown Dwarf Binary in the Galactic Disk

February 2019 • 2019ApJ...871..179C

Authors • Chung, Sun-Ju • Gould, Andrew • Skowron, Jan • Bond, Ian A. • Zhu, Wei • Albrow, Michael D. • Jung, Youn Kil • Han, Cheongho • Hwang, Kyu-Ha • Ryu, Yoon-Hyun • Shin, In-Gu • Shvartzvald, Yossi • Yee, Jennifer C. • Zang, Weicheng • Cha, Sang-Mok • Kim, Dong-Jin • Kim, Hyoun-Woo • Kim, Seung-Lee • Kim, Yun-Hak • Lee, Chung-Uk • Lee, Dong-Joo • Lee, Yongseok • Park, Byeong-Gon • Pogge, Richard W. • KMTNet Collaboration • Udalski, Andrzej • Poleski, Radek • Mróz, Przemek • Pietrukowicz, Paweł • Szymański, Michał K. • Soszyński, Igor • Kozłowski, Szymon • Ulaczyk, Krzysztof • Pawlak, Michał • OGLE Collaboration • Beichman, Charles A. • Bryden, Geoffery • Calchi Novati, Sebastiano • Carey, Sean • Gaudi, B. Scott • Henderson, Calen B. • Spitzer Team • Abe, Fumio • Barry, Richard • Bennett, David P. • Bhattacharya, Aparna • Donachie, Martin • Fukui, Akihiko • Hirao, Yuki • Itow, Yoshitaka • Kawasaki, Kohei • Kondo, Iona • Koshimoto, Naoki • Li, Man Cheung Alex • Matsubara, Yutaka • Muraki, Yasushi • Miyazaki, Shota • Nagakane, Masayuki • Ranc, Clément • Rattenbury, Nicholas J. • Suematsu, Haruno • Sullivan, Denis J. • Sumi, Takahiro • Suzuki, Daisuke • Tristram, Paul J. • Yonehara, Atsunori • MOA colllaboration

Abstract • We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very-low-mass brown dwarfs (BDs) with {M}1={21}-5+12 {M}J and {M}2={9}-2+5 {M}J, and it is located in the Galactic disk {D}{{L}}={2.85}-0.50+0.88 {kpc}. This is the fifth binary brown dwarf discovered by microlensing, and the BD binary is moving counter to the orbital motion of disk stars. Constraints on the lens physical properties come from late-time, non-caustic-crossing features of the Spitzer light curve. Thus, MOA-2016-BLG-231 shows how Spitzer plays a crucial role in resolving the nature of BDs in binary BD events with short timescales (≲10 days).

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Sebastiano Calchi Novati

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Sean Carey

Senior Scientist