Distinguishing between Planetary and Binary Interpretations of Microlensing Central Perturbations under Severe Finite-Source Effect

TL;DR

This paper identifies morphological differences in microlensing central perturbations caused by planets versus binary companions under severe finite-source effects, aiding in accurate interpretation of microlensing signals.

Contribution

It introduces a diagnostic method based on edge feature morphology to distinguish planetary signals from binary contamination in high-magnification microlensing events.

Findings

Binary-induced features form a complete annulus.

Planet-induced features appear as arc segments.

Absence of a deep dip indicates planetary origin.

Abstract

In the current strategy of microlensing planet searches focusing on high-magnification events, wide and close binaries pose important sources of contamination that imitates planetary signals. For the purpose of finding systematic differences, we compare the patterns of central perturbations induced by a planet and a binary companion under severe finite-source effect. We find that the most prominent difference shows up in the morphology of the edge features with negative excess that appear at the edge of the circle with its center located at the caustic center and a radius equivalent to the source radius. It is found that the feature induced a binary companion forms a complete annulus, while the feature induced by a planet appears as several arc segments. This difference provides a useful diagnostic for immediate iscrimination of a planet-induced perturbation from that induced by a binary companion, where the absence of a well-developed dip in the residual from the single-lensing light curve at both or either of the moments of the caustic center's entrance into and exit from the source star surface indicates that the perturbation is produced by a planetary companion. We find that that this difference is basically caused by the difference between the shapes of the central caustics induced by the two different types of companions.