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

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.