Microlensing in globular clusters: the first confirmed lens

TL;DR

This paper investigates microlensing events toward globular clusters, identifying potential cluster lenses and confirming a low-mass star lens within M22, thus providing insights into the cluster's low-mass star population.

Contribution

It presents the first confirmed microlensing lens within a globular cluster, demonstrating the feasibility of using microlensing to study low-mass stars in such clusters.

Findings

Four microlensing events may be caused by lenses in globular clusters.

A microlensing event in M22 was confirmed to be caused by a low-mass star.

The low-mass star lens in M22 has about 0.18 solar masses.

Abstract

Microlensing observations toward globular clusters could be very useful to probe their low mass star and brown dwarf content. Using the large set of microlensing events detected so far toward the Galactic centre we investigated whether for some of the observed events the lenses are located in the Galactic globular clusters. Indeed, we found that in four cases some events might be due to lenses located in the globular clusters themselves. Moreover, we discuss a microlensing event found in M22. Using the adaptive optics system NACO at ESO VLT it was possible to identify the lens, which turned out to be a low mass star of about 0.18 solar masses in the globular cluster M22 itself.