# OGLE-2015-BLG-1649Lb: A gas giant planet around a low-mass dwarf

## TL;DR

This paper reports the discovery and characterization of a gas giant exoplanet orbiting a low-mass dwarf star through microlensing, with detailed analysis constraining the system's physical parameters.

## Contribution

It presents the first detailed mass and distance measurements of a gas giant around a low-mass star via microlensing, including adaptive optics constraints and Bayesian analysis.

## Key findings

- Host star mass: 0.34 ± 0.19 M_sun
- Planet mass: 2.5^{+1.5}_{-1.4} M_Jup
- Distance: 4.23^{+1.51}_{-1.64} kpc

## Abstract

We report the discovery of an exoplanet in microlensing event OGLE-2015-BLG-1649. The planet/host-star mass ratio is $q =7.2 \times 10^{-3}$ and the projected separation normalized by the Einstein radius is $s = 0.9$. The upper limit of the lens flux is obtained from adaptive optics observations by IRCS/Subaru, which excludes the probability of a G-dwarf or more massive host star and helps to put a tighter constraint on the lens mass as well as commenting on the formation scenarios of giant planets orbiting low-mass stars. We conduct a Bayesian analysis including constraints on the lens flux to derive the probability distribution of the physical parameters of the lens system. We thereby find that the masses of the host star and planet are $M_{L} = 0.34 \pm 0.19 M_{\odot}$ and $M_{p} = 2.5^{+1.5}_{-1.4} M_{Jup}$, respectively. The distance to the system is $D_{L} = 4.23^{+1.51}_{-1.64}$kpc. The projected star-planet separation is $a_{\perp} = 2.07^{+0.65}_{-0.77}$AU. The lens-source relative proper motion of the event is quite high, at $\sim 7.1 \, {\rm mas/yr}$. Therefore, we may be able to determine the lens physical parameters uniquely or place much stronger constraints on them by measuring the color-dependent centroid shift and/or the image elongation with additional high resolution imaging already a few years from now.