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

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 Apeak ≳ 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 (Mp, Mh, DL) ~ (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.