A Solar‐like Cycle in Asymptotic Giant Branch Stars

I propose that the mechanism behind the formation of concentric semi-periodicshells found in several planetary nebulae (PNs) and proto-PNs, and around oneasymptotic giant branch (AGB) star, is a solar-like magnetic activity cycle inthe progenitor AGB stars. The time intervals between consecutive ejectionevents is about 200-1,000 years, which is assumed to be the cycle period (thefull magnetic cycle can be twice as long, as is the 22-year period in the sun).The magnetic field has no dynamical effects; it regulates the mass loss rate bythe formation of magnetic cool spots. The enhanced magnetic activity at thecycle maximum results in more magnetic cool spots, which facilitate theformation of dust, hence increasing the mass loss rate. The strong magneticactivity implies that the AGB star is spun up by a companion, via a tidal orcommon envelope interaction. The strong interaction with a stellar companionexplains the observations that the concentric semi-periodic shells are foundmainly in bipolar PNs.Comment: 10 pages, submitted to Ap