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 lightcurve model to fit for a precise mid-eclipse time and estimate the minimum separation of the two eclipsing components during the event. Our best-fit mid-eclipse time of 2458217.80943 +0.00057 −0.00050 is 19 minutes later than the prediction of Grundy et al. (2018); the minimum separation between the center of Menoetius' shadow and the center of Patroclus is 72.5 ± 0.7 km -slightly larger than the predicted 69.5 km. Using the derived lightcurves, 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.

Detection of the Irregular Shape of the Southern Limb of Menoetius from Observations of the 2017–2018 Patroclus–Menoetius Mutual Events

“…In the limit of uncertainty, the mid-eclipse time also agrees with our solution. Similarly, the solutions are compatible with the one presented in Wong & Brown (2019), an event that happened in almost the same configuration as LC20180404. The magnitude drop coincides with the result predicted by our best-fit orbital solution.…”

“…The larger uncertainty at z s is not unexpected, as the sensitivity of this filter is much smaller than for the other three. Because MuSCAT2 is obtaining these multicolor light curves simultaneously, it enables us to study differences in the four light curves and leverage these to study color variations across the surface of the components (Wong & Brown 2019) in this system. The right panel of Figure 2 shows an example for some color light curves that we built with the three magnitudes with the lowest uncertainty for that night.…”

“…The result on the orbit determination from this work has smaller uncertainties than Marchis et al (2006) and thereby supersedes this earlier work. Based on these predictions, Wong & Brown (2019) performed multiband observations of an event of the PMS showing that the minimum separation between the center of Menoetius's shadow and the center of Patroclus is 72.5 ± 0.7 km, slightly larger than predicted, as well as an upper limit of ∼0.15 mag on surface color variability across Patroclus. However, this study relies on data from a sole event, which does not allow the authors to refine the orbit of the system and study the shape and size of its components.…”

“…These events occur between binaries when the orbital plane of the system is aligned with the direction of the Sun and to an observer, and then the components take turns being eclipsed or occulted by one another. This technique has long been used for the study of binary asteroids (Pravec & Hahn 1997;Pravec et al 1998;Descamps et al 2008Descamps et al , 2009, including the study of the Patroclus-Menoetius system (Wong & Brown 2019;Berthier et al 2020). The time in which such an alignment occurs is called the mutual event season, which in the case of Patroclus-Menoetius takes place twice every ∼12 yr (the orbital period of the system around the Sun).…”