The Effect of Luminous Lens Blending in Gravitational Microlensing Experiments

The most important uncertainty in the results of current gravitational microlensing experiments comes from the difficulties of photometry caused by the blending of source stars. Recently Nemiroff pointed out that the results of microlensing experiments can also be affected by the blending of light from the lens itself if a significant fraction of lenses is composed of stars. In this paper we estimate the effects of lens blending on the optical depth determination and on the derived matter distribution toward the Galactic bulge by using realistic models of the lens matter distribution and a stellar luminosity function. We find that lens blending has a small to moderate effect on both the determination of the optical depth and the Galactic matter distribution, depending on the fraction of stellar lenses. The decrease in optical depth ranges from ~10% when half of the lenses are composed of stars, and can reach up to ~20% for the case when lenses are totally composed of stars and disk matter distribution follows a maximal disk model.