Lightcurves of Lucy Targets: Leucus and Polymele

Abstract

We present new observations from 2016 of two Jupiter Trojan asteroids that are targets for the Lucy Discovery mission. The extremely long rotation period of (11351) Leucus is confirmed and refined to a secure value of 445.732 ± 0.021 hr with photometric parameters of H r = 11.046 ± 0.003 and G r = 0.58 ± 0.02 in the SDSS r' filter. This leads to a geometric albedo of p V = 4.7%. The amplitude of the light curve was measured to be 0.61 mag, unchanged from the value of one-fourth of a revolution earlier, suggesting a low obliquity. The first light-curve observations for (15094) Polymele are also presented. This object is revealed to have a much shorter rotation period of 5.8607 ± 0.0005 hr with a very low amplitude of 0.09 mag. Its photometric parameters are H r = 11.691 ± 0.002 and G r = 0.22 ± 0.02. These values lead to a refined geometric albedo of p V = 7.3%. This object is either nearly spherical or was being viewed nearly pole-on in 2016. Further observations are required to fully determine the spin pole orientation and convex-hull shapes.