Neptune’s ring arcs: VLT/NACO near-infrared observations^⋆ and a model to explain their stability

¹ Institut de Mécanique Céleste et de Calcul de Ephémérides, UMR 8028 du CNRS, 77 avenue Denfert-Rochereau, 75014 Paris, France
² Laboratoire d’Astronomie de Lille, Université Lille 1, 1 impasse de l’observatoire, 59000 Lille, France
e-mail: Stefan.Renner@univ-lille1.fr
³ Observatoire de Paris, LESIA, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁴ Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France
⁵ Observatoire de Paris, SYRTE, 61 avenue de l’Observatoire, 75014 Paris, France
⁶ NAXYS, Namur Center for Complex Systems, Department of Mathematics, University of Namur, 5000 Namur, Belgium
⁷ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001 Santiago 19, Chile

Received: 17 May 2013
Accepted: 15 February 2014

Abstract

Context. Neptune’s incomplete ring arcs have been stable since their discovery in 1984 although these structures should be destroyed in a few months through differential Keplerian motion. Regular imaging data are needed to address the question of the arc stability.

Aims. We present the first NACO observations of Neptune’s ring arcs taken at 2.2 μm (Ks band) with the Very Large Telescope in August 2007, and propose a model for the arc stability based on co-orbital motion.

Methods. The images were aligned using the ephemerides of the satellites Proteus and Triton and were suitably co-added to enhance ring or satellite signals. Resonance theory and N-body simulations were used to model the arcs’ confinement.

Results. We derive accurate mean motion values for the arcs and Galatea and confirm the mismatch between the arcs’ position and the location of the 42:43 corotation inclination resonance. We propose a new confinement mechanism where small co-orbital satellites in equilibrium trap ring arc material. We constrain the masses and locations of these hypothetical co-orbital bodies.