The first confirmed microlens in a globular cluster

TL;DR

This paper reports the first confirmed microlens within a globular cluster, using adaptive optics to resolve the lens and source, confirming the lens as a cluster member and providing insights into stellar populations.

Contribution

The study provides the first direct imaging confirmation of a microlens in a globular cluster, combining observational data with proper motion analysis.

Findings

The lens is a 0.18 Msun dwarf star in M22.

The source is a solar-type star in the Galactic bulge.

The lens and source positions match proper motion predictions.

Abstract

In 2000 July/August a microlensing event occurred at a distance of 2.33 arcmin from the center of the globular cluster M22 (NGC6656), observed against the dense stellar field of the Milky Way bulge. We have used the adaptive optics system NACO at the ESO Very Large Telescope to resolve the two objects that participated in the event: the lens and the source. The position of the objects measured in 2011 July is in agreement with the observed relative proper motion of M22 with respect to the background bulge stars. Based on the brightness of the microlens components we find that the source is a solar-type star located at a distance of 6.0 +/-1.5 kpc in the bulge, while the lens is a 0.18 +/-0.01 Msun dwarf member of the globular cluster located at the known distance of 3.2 +/-0.2 kpc from the Sun.