Rotational Study of 5:3 and 7:4 Resonant Objects within the Main Classical Trans-Neptunian Belt

Abstract

The 5:3 and 7:4 mean motion resonances of Neptune are at 42.3 and 43.7 au, respectively, and overlap with objects in the classical trans-Neptunian belt (Kuiper Belt). We report the complete/partial lightcurves of 13 and 14 trans-Neptunian objects (TNOs) in the 5:3 and 7:4 resonances, respectively. We report a most likely contact binary in the 7:4 resonance, 2013 FR _28 , with a periodicity of 13.97 ± 0.04 hr and a lightcurve amplitude of 0.94 ± 0.02 mag. With a V-/U-shaped lightcurve, 2013 FR _28 has one of the largest well-sampled TNO amplitudes observed with ground-based observations, comparable to the well-determined contact binary 2001 QG _298 . 2013 FR _28 has a mass ratio q ∼ 1 with a density ρ ∼ 1 g cm ^−3 . We find several objects with large amplitudes and classify 2004 SC _60 , 2006 CJ _69 , and 2013 BN _82 as likely contact binaries and 2001 QF _331 , 2003 YW _179 , and 2015 FP _345 as likely elongated objects. We observe the 17:9 resonant or classical object 2003 SP _317 that we classify as a likely contact binary. A lower estimate of 10%–50% and 20%–55% for the fraction of (nearly) equal-sized contact binaries is calculated in the 5:3 and 7:4 resonances, respectively. Surface colors of 2004 SC _60 , 2013 BN _82 , 2014 OL _394 , and 2015 FP _345 have been obtained. Including these colors with ones from the literature reveals that elongated objects and contact binaries share the same ultrared surface color, except Manwë–Thorondor and 2004 SC _60 . Not only are the colors of the 7:4 and 5:3 TNOs similar to the cold classicals, but we demonstrate that the rotational properties of the 5:3 and 7:4 resonants are similar to those of the cold classicals, inferring a clear link between these subpopulations.

Keywords

• Trans-Neptunian objects
• Resonant Kuiper belt objects
• Light curves