KMT-2019-BLG-0797: Binary-lensing event occurring on a binary stellar system

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: [email protected]
² Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
³ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁴ Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁷ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁸ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
⁹ Department of Astronomy, Tsinghua University, Beijing 100084, PR China
¹⁰ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea

Received: 16 December 2020
Accepted: 2 February 2021

Abstract

Aims. We analyze the microlensing event KMT-2019-BLG-0797. The light curve of the event exhibits two anomalous features from a single-lens single-source model, and we aim to reveal the nature of the anomaly.

Methods. It is found that a model with two lenses plus a single source (2L1S model) can explain one feature of the anomaly, but the other feature cannot be explained. We test various models and find that both anomalous features can be explained by introducing an extra source to a 2L1S model (2L2S model), making the event the third confirmed case of a 2L2S event, following MOA-2010-BLG-117 and OGLE-2016-BLG-1003. It is estimated that the extra source comprises ∼4% of the I-band flux from the primary source.

Results. Interpreting the event is subject to a close–wide degeneracy. According to the close solution, the lens is a binary consisting of two brown dwarfs with masses (M₁, M₂) ∼ (0.034, 0.021) M_⊙, and it is located at a distance of D_L ∼ 8.2 kpc. According to the wide solution, on the other hand, the lens is composed of an object at the star–brown dwarf boundary and an M dwarf with masses (M₁, M₂) ∼ (0.06, 0.33) M_⊙ located at D_L ∼ 7.7 kpc. The source is composed of a late G dwarf to early K dwarf primary and an early-to-mid M dwarf companion.