KMT-2018-BLG-1988Lb: Microlensing super-Earth orbiting a low-mass disk dwarf

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Department of Astronomy, Tsinghua University, Beijing 100084, PR China
³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
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 Department of Particle Physics and Astrophysics, WeizmannInstitute of Science, Rehovot 76100, Israel
⁸ Center for Astrophysics, Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
⁹ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹⁰ Department of Astronomy & Space Science, Chungbuk National University, Cheongju 28644, Republic of Korea

Received: 24 August 2021
Accepted: 15 November 2021

Abstract

Aims. We reexamine high-magnification microlensing events in the previous data collected by the KMTNet survey with the aim of finding planetary signals that were not noticed before. In this work, we report the planetary system KMT-2018-BLG-1988L, which was found from this investigation.

Methods. The planetary signal appears as a deviation with ≲0.2 mag from a single-lens light curve and lasted for about 6 h. The deviation exhibits a pattern of a dip surrounded by weak bumps on both sides of the dip. The analysis of the lensing light curve indicates that the signal is produced by a low-mass-ratio (q ~ 4 × 10⁻⁵) planetary companion located near the Einstein ring of the host star.

Results. The mass of the planet, M_planet = 6.8_−3.5^+4.7 M_⊕ and 5.6_−2.8^+3.8 M_⊕ for the two possible solutions, estimated from the Bayesian analysis indicates that the planet is in the regime of a super-Earth. The host of the planet is a disk star with a mass of M_host = 0.47_−0.25^+0.33 M_⊙ and a distance of D_L = 4.2_−.14^+1.8 kpc. KMT-2018-BLG-1988Lb is the 18th known microlensing planet with a mass below the upper limit of a super-Earth. The fact that 15 out of the 18 known microlensing planets with masses ≲10 M_⊕ were detected in the 5 yr following the full operation of the KMTNet survey indicates that the KMTNet database is an important reservoir of very low-mass planets.