The first confirmed microlens in a globular cluster

Abstract

In 2000 July/August a microlensing event occurred at a distance of 2.33 arcmin from the center of the globular cluster M22 (NGC 6656), 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 M sun dwarf member of the globular cluster located at the known distance of 3.2 ± 0.2 kpc from the Sun.
Based on observations collected with the ESO VLT and VISTA telescopes at Paranal Observatory (ESO Programmes 087.C-0640(A) and 179.B-2002(B), respectively), and the 1.3 m Warsaw telescope at the Las Campanas Observatory of the Carnegie Institution for Science.