KMT-2021-BLG-0912Lb: a microlensing super Earth around a K-type star

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Institute of Natural and Mathematical Sciences, Massey University, Auckland 0745, New Zealand
³ Center for Astrophysics | Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
⁴ Department of Astronomy, Tsinghua University, Beijing 100084, PR China
⁵ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁶ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁹ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
¹⁰ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹¹ Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
¹² Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹³ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁴ Department of Astronomy, University of Maryland, College Park, MD 2074, USA
¹⁵ Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
¹⁶ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁷ Instituto de Astrofśica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁸ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁹ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁰ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
²¹ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
²² Department of Physics, The Catholic University of America, Washington, DC 20064, USA
²³ University of Canterbury Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand
²⁴ Kumeu Observatory, Kumeu, New Zealand
²⁵ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Road 5, Hai Dian District, Beijing 100871, PR China
²⁶ Possum Observatory, Patutahi, New Zealand
²⁷ Centre for Astrophysics, University of Southern Queensland, Toowoomba, Queensland 4350, Australia
²⁸ Department of Astronomy, School of Physics, Peking University, Yi He Yuan Road 5, Hai Dian District, Beijing 100871, PR China
²⁹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
³⁰ School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 6997801, Israel
³¹ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA

Received: 21 October 2021
Accepted: 8 November 2021

Abstract

Aims. The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly.

Methods. We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found underthe assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of binary stars (1L2S model). The 1L2S model is ruled out based on the contradiction that the faint source companion is bigger than its primary, and one of the 2L1S solutions is excluded from the combination of the poorer fit, blending constraint, and lower overall probability, leaving two surviving solutions with the planet/host mass ratios of q ~ 2.8 × 10⁻⁵ and ~ 1.1 × 10⁻⁵. A subtle central deviation supports the possibility of a tertiary lens component, either a binary companion to the host with a very large or small separation, or a second planet lying near the Einstein ring, but it is difficult to claim a secure detection due to the marginal improvement of the fit, lack of consistency among different data sets, and difficulty in uniquely specifying the nature of the tertiary component.

Results. With the observables of the event, it is estimated that the masses of the planet and host are ~ (6.9 M_⊕, 0.75 M_⊙) according to one solution and~(2.8 M_⊕, 0.80 M_⊙) according to the other, indicating that the planet is a super Earth around a K-type star, regardless of the solution. The fact that 16 (including the one reported in this work) out of 19 microlensing planets with M ≲ 10 M_⊕ were detected during the last 6 yr nicely demonstrates the importance of high-cadence global surveys in detecting very low-mass planets.