THE PHYSICAL NATURE OF OGLE GRAVITATIONAL LENSES

A model fitting analysis is performed for six light curves resulting f rom gravitational microlensing of Galactic bulge stars, obtained durin g the Optical Gravitational Lensing Experiment. For three of these eve nts, allowing for radiation from the gravitational lens yields a bette r lit than provided by models with a dark, compact lens or with a lens formed of a cluster of weakly interacting massive particles. The char acteristics and distances of the lensing and lensed stars are estimate d for these events. It is proposed that ordinary late-type dwarfs can play the role of the gravitational lens in about half the bulge stella r microlensing events. This would make it possible to partially explai n the observed excess in the optical depth to microlensing for bulge s tars over that predicted by existing theoretical models for the distri bution of massive compact objects in the Galactic halo.