Dynamo-Driven Outflows in Pre-Planetary Nebulae

The plethora of asymmetric planetary nebulae and the curiously high momenta of pre-planetary nebula outflows suggest that rotational energy is extracted from the engines. Magneto-rotational outflows driven by dynamos might be operating therein. I summarize scenarios involving (a) an isolated AGB star and (b) a binary. The efficacy of (a) requires re-establishing differential rotation over the AGB star's lifetime, whereas (b) delivers the angular momentum at the end of the AGB phase when needed, and may involve turbulent disks. Both can produce fields that drive outflows of the required mechanical luminosity and momentum, though weak points and open questions require further study.