Angle-action variables for orbits trapped at a Lindblad resonance
  The conventional approach to orbit trapping at Lindblad resonances via a
pendulum equation fails when the parent of the trapped orbits is too circular.
The problem is explained and resolved in the context of the Torus Mapper and a
realistic Galaxy model. Tori are computed for orbits trapped at both the inner
and outer Lindblad resonances of our Galaxy. At the outer Lindblad resonance,
orbits are quasiperiodic and can be accurately fitted by torus mapping. At the
inner Lindblad resonance, orbits are significantly chaotic although far from
ergodic, and each orbit explores a small range of tori obtained by torus
mapping.
