Blending in Future Space‐based Microlensing Surveys

We investigate the effect of blending in future gravitational microlensingsurveys by carrying out simulation of Galactic bulge microlensing events to bedetected from a proposed space-based lensing survey. From this simulation, wefind that the contribution of the flux from background stars to the totalblended flux will be equivalent to that from the lens itself despite thegreatly improved resolution from space observations, implying thatcharacterizing lenses from the analysis of the blended flux would not be easy.As a method to isolate events for which most of the blended flux isattributable to the lens, we propose to use astrometric information of sourcestar image centroid motion. For the sample of events obtained by imposing acriterion that the centroid shift should be less than three times of theastrometric uncertainty among the events for which blending is noticed withblended light fractions $f_{\rm B}>0.2$, we estimate that the contamination ofthe blended flux by background stars will be less than 20% for most ($\sim90%$) of the sample events. The expected rate of these events is $\gtrsim 700$events/yr, which is large enough for the statistical analysis of the lenspopulations.Comment: total 6 pages, including 5 figures, ApJ, in pres