Planetary nebulae classification

The classification is based primarily on the morphologies of the different planetary nebulae, assuming that binary companions, stellar or substellar, are necessary in order to have axisymmetrical mass loss on the asymptotic giant branch. I propose four evolutionary classes, according to the binary-model hypothesis: (1) Progenitors of planetary nebulae that did not interact with any companion.

These amount to ~10% of all planetary nebulae. (2) Progenitors that interact with stellar companions that avoided a common envelope, 11^+2^_-3_% of all nebulae. (3) Progenitors that interact with stellar companions via a common envelope phase, 23^+11^_-5_% of all nebulae.