Shaping Proto-Planetary and Young Planetary Nebulae with Collimated Fast   Winds
  Using two-dimensional hydrodynamical simulations, we investigate the interaction of a collimated fast wind (CFW) interacting with a spherical asymptotic giant branch (AGB) wind as the mechanism for shaping proto-planetary nebulae and young planetary nebulae. In particular, we compare our simulations to the observations of an evolved PPN with multiple, highly collimated lobes, CRL 618. 
Chin-Fei Lee and Raghvendra Sahai