MOA-2010-BLG-523: "failed planet" = RS CVn STAR

Abstract

The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of anAmax ~ 265 high-magnificationmicrolensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the firstspectroscopically confirmed RS CVn star discovered in the Galactic bulge.