Mass Measurements of Isolated Objects from Space-based Microlensing

TL;DR

This study demonstrates how combined ground and space observations enable precise mass and distance measurements of isolated objects like brown dwarfs and stars through microlensing.

Contribution

It provides the first mass and distance measurements of isolated objects from space-based microlensing data, highlighting the importance of simultaneous observations.

Findings

The lens in OGLE-2015-BLG-1268 is a brown dwarf of about 45 Jupiter masses.

The lens in OGLE-2015-BLG-0763 is a star of about 0.5 solar masses.

Simultaneous ground and space observations significantly improve mass measurement accuracy.

Abstract

We report on the mass and distance measurements of two single-lens events from the 2015 \emph{Spitzer} microlensing campaign. With both finite-source effect and microlens parallax measurements, we find that the lens of OGLE-2015-BLG-1268 is very likely a brown dwarf. Assuming that the source star lies behind the same amount of dust as the Bulge red clump, we find the lens is a $45\pm7$ $M_{\rm J}$ brown dwarf at $5.9\pm1.0$ kpc. The lens of of the second event, OGLE-2015-BLG-0763, is a $0.50\pm0.04$ $M_\odot$ star at $6.9\pm1.0$ kpc. We show that the probability to definitively measure the mass of isolated microlenses is dramatically increased once simultaneous ground- and space-based observations are conducted.