Multiband Photometry of a Patroclus–Menoetius Mutual Event: Constraints on Surface Heterogeneity

Abstract

We present the first complete multiband observations of a binary asteroid mutual event. We obtained high-cadence, high-signal-to-noise photometry of the UT 2018 April 9 inferior shadowing event in the Jupiter Trojan binary system Patroclus–Menoetius in four Sloan bands—g', r', i', and z'. We use an eclipse light-curve model to fit for a precise mideclipse time and estimate the minimum separation of the two eclipsing components during the event. Our best-fit mideclipse time of 2458217.80943^(+0.00057)_(−0.00050) is 19 minutes later than the prediction of Grundy et al. The minimum separation between the center of Menoetius's shadow and the center of Patroclus is 72.5 ± 0.7 km—slightly larger than the predicted 69.5 km. Using the derived light curves, we find no evidence for significant albedo variations or large-scale topographic features on the Earth-facing hemisphere and limb of Patroclus. We also apply the technique of eclipse mapping to place an upper bound of ~0.15 mag on wide-scale surface color variability across Patroclus.