KMT-2018-BLG-1025Lb: microlensing super-Earth planet orbiting a low-mass star^★

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
³ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁴ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁵ Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁸ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁹ Center for Astrophysics, Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
¹⁰ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹¹ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹² Department of Astronomy & Space Science, Chungbuk National University, Cheongju 28644, Republic of Korea
¹³ Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea
¹⁴ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
¹⁵ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK

Received: 31 October 2020
Accepted: 3 February 2021

Abstract

Aims. We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data.

Methods. For this purpose, we conducted a systematic inspection of high-magnification microlensing events, with peak magnifications of A_peak ≳ 30, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identified an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens.

Results. We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close–wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is q ~ 0.8 × 10⁻⁴ for solution A and q ~ 1.6 × 10⁻⁴ for solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are (M_p, M_h, D_L) ~ (6.1 M_⊕, 0.22 M_⊙, 6.7 kpc) for solution A and ~(4.4 M_⊕, 0.08 M_⊙, 7.5 kpc) for solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar System’s ice giants, which were discovered by microlensing.