Planetary Lensing Signals of High-Magnification Events under Severe Finite-Source Effect

TL;DR

This study explores how finite-source effects influence planetary-lensing signals in high-magnification events, revealing that certain perturbations persist even with large sources and identifying characteristic features useful for detecting planetary companions.

Contribution

It demonstrates that finite-source effects have a weak dependency on caustic shape and identifies distinctive perturbation patterns for diagnosing planetary companions.

Findings

Perturbations with ≥5% magnification excess survive when the source is about 4 times larger than the caustic.

Characteristic circular features in perturbation patterns aid in planetary detection.

Short-duration perturbations with flat residuals are signatures of finite-source effects.

Abstract

We investigate the effect of a finite source on the planetary-lensing signals of high-magnification events. From this, we find that the dependency of the finite-source effect on the caustic shape is weak and perturbations survive even when the source is substantially bigger than the caustic. Specifically, we find that perturbations with fractional magnification excess $\geq 5%$ survive when the source star is roughly 4 times bigger than the caustic. We also find characteristic features that commonly appear in the perturbation patterns of planetary lens systems affected by severe finite-source effect and thus can be used for the diagnosis of the existence of a companion. These features form in and around a circle with its center located at the caustic center and a radius corresponding to that of the source star. The light curve of an event where the source crosses these features will exhibit a distinctive signal that is characterized by short-duration perturbations of either positive or negative excess and a flat residual region between these short-duration perturbations.