Color-shift measurement in microlensing-induced stellar variation from future space-based surveys

If a microlensing event is caused by a star, the event can exhibit a change in color due to the light from the lens. In previous and current lensing surveys, these color shifts could not be used to constrain the lens population, because the blended light responsible for the shift is mostly attributable to nearby background stars rather than the lens. However, events observed in future space-based surveys will not suffer from blending, and thus the color information can be used to constrain the lenses. In this paper, we demonstrate the usefulness of future surveys in measuring color shifts. By conducting a simulation of Galactic lensing events based on the specifications for a proposed space-based lensing survey, we estimate that shifts in R-H color will be measurable at the 5 sigma level for similar to 12% of events that occur for source stars with apparent magnitudes brighter than J = 22.5. Color-shifted events tend to have high magnification, and the lenses will have brightnesses equivalent to those of the source stars. The timescales of the color-shifted events tend to be longer than those without color shifts. From the mass distribution of lenses, we find that most of the color-shifted events will be produced by stellar lenses with spectral types down to mid M-type main-sequence stars.