Results from a Survey of Gravitational Microlensing toward M31

Abstract

We describe the results of a search for microlensing events affecting stars in the outer bulge and inner disk of M31, due both to masses in M31 and the Galaxy. These observations, from 1994 and 1995 on the Vatican Advanced Technology Telescope and KPNO 4 m telescope, are sufficient to rule out masses in the range ~0.003-0.08 M☉ as the primary constituents of the mass of M31 toward this field. Furthermore, we find six candidate events consistent with microlensing as a result of masses of about 1 M☉, but we suspect that some of these may be cases in which long-period red supergiant variables may be mistaken for microlensing events. Coverage from anticipated data should be helpful in determining whether these sources maintain a constant baseline, and therefore they are best described by microlensing events.