Color-Shift Measurement in Microlensing-Induced Stellar Variation from Future Space-Based Surveys

TL;DR

Future space-based microlensing surveys can effectively measure color shifts caused by stellar lenses, enabling better constraints on lens populations by utilizing the absence of blending in these observations.

Contribution

This paper demonstrates the potential of future space-based surveys to measure color shifts in microlensing events, which were not feasible in previous surveys due to blending issues.

Findings

Color shifts can be measured at 5σ for about 12% of events with bright source stars.

Color-shifted events are associated with high magnifications and similar brightness lenses and sources.

Most color-shifted events are caused by stellar lenses down to mid M-type stars.

Abstract

If a microlensing event is caused by a star, the event can exhibit change in color due to the light from the lens. In the previous and current lensing surveys, the color shift could not be used to constrain the lens population because the blended light responsible for the color shift is mostly attributed to nearby background stars rather than the lens. However, events to be observed in future space-based surveys do not suffer from blending and thus the color information can be used to constrain lenses. In this paper, we demonstrate the usefulness of future surveys in measuring color shifts. By conducting simulation of galactic lensing events based on the specification of a proposed space-based lensing survey, we estimate that the shift in the color of $R-H$ will be measured at 5$\sigma$ level for $\sim 12%$ of events that occur on source stars with apparent magnitudes brighter than $J=22.5$. Color-shifted events tend to have high magnifications and the lenses will have brightnesses equivalent to those of source stars. The time scales 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.