Lightcurves and Rotations of Trans-Neptunian Objects in the 2:1 Mean Motion Resonance with Neptune

Audrey Thirouin, Scott S. Sheppard

Published 2022-06-20Version 1

We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune's 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey's goal is to find objects displaying a large lightcurve amplitude which is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a significant short-term lightcurve amplitude: 2002 VD$_{130}$ and (531074) 2012 DX$_{98}$. The full lightcurve of 2012 DX$_{98}$ infers a periodicity of 20.80$\pm$0.06h and amplitude of 0.56$\pm$0.03mag whereas 2002 VD$_{130}$ rotates in 9.85$\pm$0.07h with a 0.31$\pm$0.04mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX$_{98}$ as a likely contact binary, but 2002 VD$_{130}$ as a likely single elongated object. Based on our sample and the lightcurves reported in the literature, we estimate the lower percentage of nearly equal-sized contact binaries at only 7-14$\%$ in the 2:1 resonance, which is comparable to the low fraction reported for the dynamically Cold Classical trans-Neptunian objects. This low contact binary fraction in the 2:1 Neptune resonance is consistent with the lower estimate of the recent numerical modeling. We report the Sloan g', r', i' surface colors of 2002 VD$_{130}$ which is an ultra-red TNO whereas 2012 DX$_{98}$ is a very red object based on published surface colors.