Keck, gemini, and palomar 200-inch visible photometry of red and very-red neptunian trojans

Neptunian Trojans (NTs), trans-Neptunian objects in 1:1 mean-motion resonance with Neptune, are generally thought to have been captured from the original protoplanetary disk into co-orbital ice giant during its outward migration. It is possible, therefore, that colour distribution of NTs a constraint on location any transition zones may present disk. In support this possible test, we obtained $g$, $r$, and $i$-band observations 18 NTs, more than doubling sample known visible colours 31 objects. Out combined sample, found $\approx$4 $g$-$i$ $>$1.2 mags placing them very red (VR) category as typically defined. We find, without taking observational selection effects account, NT statistically distinct other dynamical classes. The optical Jovian shown be less similar previously claimed additional VR NTs. presence among suggest zone was interior 30-35 au.