Distinguishing central perturbations by binary stellar and planetary systems under the moderately strong finite-source effect

TL;DR

This paper identifies distinctive features in high-magnification microlensing events caused by binary and planetary systems under finite-source effects, enabling differentiation between the two despite degeneracies.

Contribution

It introduces specific characteristic features in central perturbations that distinguish binary from planetary microlensing events under certain conditions.

Findings

Binary systems show a constant feature range when caustic size is 1.5-1.9 times the source diameter.

Planetary systems' features vary with the planet/primary mass ratio.

Binary-lensing features can be distinguished from planetary-lensing despite finite-source effects.

Abstract

We investigate high-magnification events caused by wide binary stellar and planetary systems under the moderately strong finite-source effect where the diameter of the source star is comparable with the caustics induced by a binary companion and a planet. From this investigation, we find that a characteristic feature in the central perturbations induced by the binary systems commonly appears in a constant range where the size of the caustic induced by the binary companion is between 1.5 and 1.9 times of the diameter of the source, whereas in the central perturbations induced by the planetary systems the feature commonly appears in a range where the ratio of the size of the caustic induced by the planet to the source diameter changes with the planet/primary mass ratio. High-magnification events caused by the binary and planetary systems with the characteristic feature produce a distinctive short-duration bump in the residuals from the single-lensing light curve, where the bump occurs near the time of peak magnification of the events. Because of a well-known planet/binary degeneracy, we compare binary- and planetary-lensing events with the short-duration bump in the residuals. As a result, we find the features of the binary-lensing events that are discriminated from the planetary-lensing events despite the moderately strong finite-source effect and thus can be used to immediately distinguish between the binary and planetary companions. We also find the feature that appears only in binary-lensing events with a very low mass ratio or planetary-lensing events. This implies that the lens systems with the feature have a very low mass binary companion (such as a brown dwarf) or a planet.