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

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.