OGLE-2005-BLG-153: Microlensing Discovery and Characterization of A Very Low Mass Binary

TL;DR

This paper reports the discovery of a very low-mass binary star system via microlensing, providing a new method to measure the mass function of faint, low-mass binaries in the galaxy.

Contribution

It presents the first microlensing-based measurement of a low-mass binary's component masses near the hydrogen-burning limit.

Findings

Binary components have masses of approximately 0.10 and 0.09 solar masses.

Microlensing can measure low-mass binary masses independently of luminosity biases.

Demonstrates microlensing as a tool for studying the galactic low-mass binary population.

Abstract

The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very low-mass stars just above the hydrogen-burning limit. From the combined measurements of the Einstein radius and microlens parallax, we measure the masses of the binary components of $0.10\pm 0.01\ M_\odot$ and $0.09\pm 0.01\ M_\odot$. This discovery demonstrates that microlensing will provide a method to measure the mass function of all Galactic populations of very low mass binaries that is independent of the biases caused by the luminosity of the population.