MOA-2019-BLG-008Lb: a new microlensing detection of an object at the planet/brown dwarf boundary

TL;DR

This paper reports the detection of a planetary-mass object near the planet/brown dwarf boundary through microlensing, using parallax measurements and galactic models to estimate its properties.

Contribution

It presents a new microlensing detection of a substellar companion at the planet/brown dwarf boundary and demonstrates the use of galactic models to infer physical characteristics.

Findings

The companion has a mass of about 30 MJup, near the brown dwarf boundary.

The lens is likely a main sequence star in the Galactic Bulge.

Future high-resolution imaging can confirm the system's nature.

Abstract

We report on the observations, analysis and interpretation of the microlensing event MOA-2019- BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite source effects were observed. Therefore the angular Einstein ring radius cannot be measured from the light curve alone. However, the large event duration, t E about 80 days, allows a precise measurement of the microlensing parallax. In addition to the constraints on the angular radius and the apparent brightness I s of the source, we employ the Besancon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two Galactic models: the companion is likely a resident of the brown dwarf desert with a mass Mp about 30 MJup and the host is a main sequence dwarf star. The lens lies along the line of sight to the Galactic Bulge, at a distance of less then4 kpc. We estimate that in about 10 years, the lens and source will be separated by 55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground or space-based observatories.