Removing the Microlensing Blending-Parallax Degeneracy Using Source Variability

Microlensing event MACHO 97-SMC-1 is one of the rare microlensing events for which the source is a variable star, simply because most variable stars are systematically eliminated from microlensing studies. Using observational data for this event, we show that the intrinsic variability of a microlensed star is a powerful tool for constraining the nature of the lens by breaking the degeneracy between the microlens parallax and the blended light. We also present a statistical test for discriminating the location of the lens based on the χ2 contours of the vector 𝚲, the inverse of the projected velocity. We find that while SMC self-lensing is somewhat favored over halo lensing, neither location can be ruled out with good confidence.