Rings around irregular bodies

Aims . Our goal was to understand how collisional rings can be confined near second-order SORs in spite of the fact that they force self-intersecting streamlines. Methods . We used full 3D numerical simulations that treat rings of inelastically colliding particles orbiting nonaxisymmetric central bodies, characterized by a dimensionless mass anomaly parameter µ . While most of our simulations ignore self-gravity, a few runs include gravitational interactions between particles, providing preliminary results on the effect of self-gravity on the ring confinement. Results . The 1/3 SOR can confine ring material, by transferring the forced resonant mode into free Lindblad modes. We derived a criterion ensuring that the 1/3 SOR counteracts viscous spreading. It reads kµ 2 ≳ τR 2 , where k is a dimensionless coefficient, τ is the ring optical depth, and R is the particle radius. Expressing R in terms of the radius of the synchronous orbit, we obtain k ∼ 4 × 10 −5 for the 1/3 SOR acting on nongravitating rings. Assuming meter-sized ring particles, and τ ∼ 1, this requires a threshold value µ ≳ 10 −3 in Chariklo’s case. The confinement is not permanent as a slow outward leakage of particles is observed in our simulations. This leakage can be halted by an outside moonlet with a mass of ∼10 −7 –10 −6 relative to Chariklo, corresponding to subkilometer-sized objects. With self-gravity, the ring viscosity increases by a factor of a few in low- τ rings due to gravitational encounters. For large τ , self-gravity wakes enhance the viscosity ν by a factor of ∼100 compared to a nongravitating ring, requiring ∼tenfold larger µ values since the threshold value increases proportionally to v .