The origin of rR 1 ring structures in barred galaxies

We propose a new theory for the formation of rR1 ring structures, i.e. for ring structures with both an inner and an outer ring, the latter having the form of "8". We propose that these rings are formed by material from the stable and unstable invariant manifolds associated with the Lyapunov orbits around the equilibrium points of a barred galaxy. We discuss the shape and velocity structure of the rings thus formed and argue that they are in agreement with the observed properties of rR1 structures.