Photometry of Kuiper belt objects in inner and outer mean motion resonances with Neptune

Abstract

We present a time-resolved photometric survey of Kuiper Belt Objects (KBOs) trapped in the inner and outer Neptune resonances. Lightcurves and rotational properties provide constraints on the shapes, internal structures, collisional histories, and formation environments of these primitive bodies. Our survey was conducted using the Magellan-Baade telescope and the Lowell Discovery Telescope, allowing us to go fainter than past works and yielding lightcurve studies for 41 KBOs in the 1:1, 5:4, 4:3, 11:5, 7:3, 12:5, and 5:2 resonances. We obtained complete lightcurves for objects displaying large amplitudes, with two KBOs in the 5:2 resonance (2001 XQ$_{254}$, 2013 RZ$_{108}$), one object in the 7:3 (2013 TJ$_{159}$), and one object in the 12:5 (2015 AR$_{293}$). Their lightcurve amplitudes range from 0.26 to 0.46mag, with rotational periods between 5.35 and 11.63 h. 2013 TJ$_{159}$ has the fastest rotation, largest amplitude, and most asymmetric lightcurve in our sample. Combining our results with published studies, we find that inner and outer resonant KBOs generally display lower lightcurve amplitudes than the dynamically Cold Classical population and the 5:3 and 7:4 resonances. The absence of the amplitude--period trends observed in those populations, and their surface color distributions, further suggests that inner and outer resonances do not share the same origin or evolutionary history as the Cold Classicals and overlapping resonances. Based on the literature and our survey, only one nearly equal-sized contact binary, 2004 TT$_{357}$, is currently known among the surveyed populations, implying a lower limit to the contact binary fraction of $\sim$12-15% in the 5:2 resonance.