Effects of stellar mass loss on the formation of planetary nebulae.

Models of planetary-nebula (PN) formation involving stellar-mass-loss processes are reviewed. Mass loss in the red giant (RG) progenitors of PN is examined, and an empirical formula for estimating it is derived. The importance of steady mass loss for the evolution of asymptotic-giant-branch stars is stressed, and it is shown that their circumstellar envelopes are probably not formed by sudden activity during short (less than about 1000-year) periods. Calculations of PN-central-star winds and the interaction of stellar winds are compared with models of PN formation by sudden ejection and with observational data from GL 618, the most likely proto-PN star. It is suggested that RG evolution is terminated by a steady wind over a period longer than 10,000 years, and that PN evolution and formation is significantly affected, if not dominated, by RG and central-star wind interactions.