KMT-2018-BLG-0748Lb: Sub-Saturn Microlensing Planet Orbiting an Ultracool Host

TL;DR

This paper reports the discovery of a sub-Saturn mass planet orbiting an ultracool dwarf via microlensing, highlighting the potential for detecting planets around very low-mass hosts.

Contribution

The study presents the first microlensing detection of a sub-Saturn planet orbiting an ultracool dwarf host, with detailed analysis of the event and host properties.

Findings

Planet mass estimated at ~0.18 Jupiter masses.

Host mass near the star/brown dwarf boundary.

Event characterized by short timescale and small Einstein radius.

Abstract

We announce the discovery of a microlensing planetary system, in which a sub-Saturn planet is orbiting an ultracool dwarf host. We detect the planetary system by analyzing the short-timescale ($t_{\rm E}\sim 4.4$~days) lensing event KMT-2018-BLG-0748. The central part of the light curve exhibits asymmetry due to the negative deviations in the rising part and the positive deviations in the falling part. We find that the deviations are explained by a binary-lens model with a mass ratio between the lens components of $q\sim 2\times 10^{-3}$. The short event timescale together with the small angular Einstein radius, $\theta_{\rm E}\sim 0.11$~mas, indicate that the mass of the planet host is very small. The Bayesian analysis conducted under the assumption that the planet frequency is independent of the host mass indicates that the mass of the planet is $M_{\rm p}=0.18^{+0.29}_{-0.10}~M_{\rm J}$, and the mass of the host, $M_{\rm h}= 0.087^{+0.138}_{-0.047}~M_\odot$, is near the star/brown dwarf boundary, but the estimated host mass is sensitive to the assumption about the planet hosting probability. High-resolution follow-up observations would lead to revealing the nature of the planet host.