A Planetary lensing feature in caustic-crossing high-magnification microlensing events

TL;DR

This paper identifies a distinctive feature in the light curves of high-magnification microlensing events caused by planets versus binary stars, enabling quick differentiation without extensive modeling.

Contribution

It introduces a novel method to distinguish planetary from binary lensing events based on the shape of the interpeak region in caustic-crossing light curves.

Findings

Planetary-lensing events show a convex or boxy interpeak structure.

Binary-lensing events exhibit a concave interpeak structure.

Finite source effects influence the interpeak shape depending on the planet-star mass ratio.

Abstract

Current microlensing follow-up observations focus on high-magnification events because of the high efficiency of planet detection. However, central perturbations of high-magnification events caused by a planet can also be produced by a very close or a very wide binary companion, and the two kinds of central perturbations are not generally distinguished without time consuming detailed modeling (a planet-binary degeneracy). Hence, it is important to resolve the planet-binary degeneracy that occurs in high-magnification events. In this paper, we investigate caustic-crossing high-magnification events caused by a planet and a wide binary companion. From this study, we find that because of the different magnification excess patterns inside the central caustics induced by the planet and the binary companion, the light curves of the caustic-crossing planetary-lensing events exhibit a feature that is discriminated from those of the caustic-crossing binary-lensing events, and the feature can be used to immediately distinguish between the planetary and binary companions. The planetary-lensing feature appears in the interpeak region between the two peaks of the caustic-crossings. The structure of the interpeak region for the planetary-lensing events is smooth and convex or boxy, whereas the structure for the binary-lensing events is smooth and concave. We also investigate the effect of a finite background source star on the planetary-lensing feature in the caustic-crossing high-magnification events. From this, we find that the convex-shaped interpeak structure appears in a certain range that changes with the mass ratio of the planet to the planet-hosting star.