Correcting for Blending Problems in Gravitational Microlensing Events by UsingHubbleSpaceTelescope

The biggest uncertainty in determining microlensing parameters comes from theblending of source star images because the current experiments are beingcarried out toward very dense star fields: the Galactic bulge and MagellanicClouds. The experiments try to correct the blending effects for individualevents by introducing an additional lensing parameter, the residual flux, butthis method suffers from very large uncertainties in the derived lensingparameters due to the degeneracies among the parameters. In this paper, Ipropose to use the Hubble Space Telescope (HST) to correct blending effects.With the high resolving power of the HST combined with the color informationfrom ground-based observations, one can uniquely identify the lensed sourcestar in the blended seeing disk, and thus the uncertainty in the derived timescale can be significantly reduced.Comment: 18 pages including 2 tables and 3 figures, submitted to Ap