Properties of microlensing events by wide separation planets with a moon

TL;DR

This paper studies microlensing events caused by wide separation planets with moons, revealing that moon features produce short perturbations distinguishable from planetary signals, with implications for detecting exomoons.

Contribution

It provides a detailed analysis of moon-induced features in microlensing light curves for wide separation planetary systems, including effects of finite source size and caustic separation.

Findings

Moon features appear as short perturbations on asymmetric light curves.

The asymmetry due to bound planets is noticeable up to ~20 AU.

Moon perturbations dominate as star-planet separation increases.

Abstract

We investigate the properties of microlensing events caused by planetary systems where planets with a moon are widely separated from their host stars. From this investigation, we find that the moon feature generally appears as an very short-duration perturbation on the smooth asymmetric light curve of the lensing event induced by the wide separation planet; thus it can be easily discriminated from the planet feature responsible for the overall asymmetric light curve. For typical Galactic lensing events with the Einstein radius of $\sim 2$ AU, the asymmetry of the light curves due to bound planets can be noticed up to $\sim 20$AU. We also find that the perturbations of the wide planetary systems become dominated by the moon as the projected star-planet separation increases, and eventually the light curves of events produced by the systems appear as the single lensing light curve of the planet itself with a very short-duration perturbation induced by the moon, which is a representative light curve of the event induced by a star and a planet, except on the Einstein timescale of the planet. We also study the effect of a finite source star on the moon feature in the wide planetary lensing events. From this study, we find that when the lunar caustic is sufficiently separated from the planetary caustic, the lower limit on the ratio of the lunar caustic size to the source radius causing a $\geq 5\%$ lunar deviation depends mostly on the projected planet-moon separation regardless of the moon/star mass ratio, and it decreases as the planet-moon separation becomes smaller or larger than the planetary Einstein radius.