IS THERE A CONNECTION BETWEEN THERMAL PULSES AND PNE HALOS - ON THE WAY TO AN ANSWER

We explore the hypothesis that the shells and halos of planetary nebul ae (PNe) are formed during multiple phases of enhanced mass loss (supe rwinds). These superwinds occur on the Asymptotic Giant Branch (AGB) a nd are terminated by thermal pulses. Using recent results from models of AGB star evolution by Vassiliadis & Wood (1993) and published data for halos of PNe we compare the theoretical times between thermal puls es with the observed dynamical times derived from halo separations for a small but carefully selected sample of PNe. We find that the theore tical and observational time scales are within an order of magnitude f rom each other. Considering the large experimental errors, mainly due to uncertainties in distances, this is an encouraging result. However, a larger sample of PNe halos are needed to prove that multiple superw inds are responsible for PNe halos.