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

Abstract

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 that 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 VD130 and (531074) 2012 DX98. The full lightcurve of 2012 DX98 infers a periodicity of 20.80 ± 0.06 hr and amplitude of 0.56 ± 0.03 mag, whereas 2002 VD130 rotates in 9.85 ± 0.07 hr with a 0.31 ± 0.04 mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX98 as a likely contact binary but 2002 VD130 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 TNOs. 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′, and i′ surface colors of 2002 VD130, which is an ultra-red TNO whereas 2012 DX98 is a very red object based on published surface colors.