KMT-2018-BLG-1988Lb: microlensing super-Earth orbiting a low-mass disk
  dwarf
  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 that was found from this investigation. The planetary signal
appears as a deviation with $\lesssim 0.2$~mag from a single-lens light curve
and lasted for about 6 hours. 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 ($q\sim
4\times 10^{-5}$) planetary companion located near the Einstein ring of the
host star. The mass of the planet, $M_{\rm planet}=6.8^{+4.7}_{-3.5}~M_\oplus$
and $5.6^{+3.8}_{-2.8}~M_\oplus$ 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 $M_{\rm host}
= 0.47^{+0.33}_{-0.25}~M_\odot$ and a distance of $D_{\rm L}=
4.2^{+1.8}_{-.14}$~kpc. KMT-2018-BLG-1988Lb is the seventeenth microlensing
planet with a mass below the upper limit of a super-Earth. The fact that 14 out
of 17 microlensing planets with masses $\lesssim 10~M_\oplus$ were detected
during the last 5 years since the full operation of the KMTNet survey indicates
that the KMTNet database is an important reservoir of very low-mass planets.
