Identification of the Microlens in Event MACHO-LMC-20

We report on the identification of the lens responsible for microlensing event MACHO-LMC-20. As part of a Spitzer IRAC program conducting mid-infrared follow-up of the MACHO Large Magellanic Cloud microlensing fields, we discovered a significant flux excess at the position of the source star for this event. These data, in combination with high-resolution near-infrared Magellan PANIC data, have allowed us to classify the lens as an early M dwarf in the thick disk of the Milky Way, at a distance of 62 kpc. This is only the second microlens to have been identified, the first also being a M dwarf star in the disk. Together, these two events are still consistent with the expected frequency of nearby stars in the Milky Way thin and thick disks acting as lenses.