OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax

September 2022 • 2022AJ....164..102M

Authors • Malpas, Amber • Albrow, Michael D. • Yee, Jennifer C. • Gould, Andrew • Udalski, Andrzej • Martin, Antonio Herrera • Beichman, Charles A. • Bryden, Geoffery • Novati, Sebastiano Calchi • Carey, Sean • Henderson, Calen B. • Gaudi, B. Scott • Shvartzvald, Yossi • Zhu, Wei • Cha, Sang-Mok • Chung, Sun-Ju • Han, Cheongho • Hwang, Kyu-Ha • Jung, Youn Kil • Kim, Dong-Jin • Kim, Hyoun-Woo • Kim, Seung-Lee • Lee, Chung-Uk • Lee, Dong-Joo • Lee, Yongseok • Park, Byeong-Gon • Pogge, Richard W. • Ryu, Yoon-Hyun • Shin, In-Gu • Zang, Weicheng • Iwanek, Patryk • Kozłowski, Szymon • Mróz, Przemek • Pietrukowicz, Paweł • Poleski, Radoslaw • Rybicki, Krzysztof A. • Skowron, Jan • Soszyński, Igor • Szymański, Michał K. • Ulaczyk, Krzysztof • OGLE Collaboration

Abstract • We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ( ${M}_{1}={170}_{-50}^{+40}{M}_{J}$ and ${M}_{2}={110}_{-30}^{+20}{M}_{J}$ ), or well below ( ${M}_{1}={22.5}_{-0.4}^{+0.7}{M}_{J}$ and ${M}_{2}={13.3}_{-0.3}^{+0.4}{M}_{J}$ ) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope.


IPAC Authors


Sebastiano Calchi Novati

Associate Scientist

Sean Carey

Senior Scientist