RADIATION GASDYNAMICS OF PLANETARY-NEBULAE .6. THE EVOLUTION OF ASPHERICAL PLANETARY-NEBULAE

This paper reports the results of the numerical study of the formation of aspherical planetary nebulae through the generalized interacting w inds model, faking into account the effects caused by the evolving cen tral star and fast wind. The results show for the first time that asph erical nebulae do form within the required time-scale. Consideration o f the development of the nebula shows that in the early stages it is t he ionization of the aspherical AGB wind that contributes considerably to the shaping of the nebula. Furthermore, the passing through of the ionization front may modify the density distribution in the slow wind , leading to the formation of a surrounding envelope, and sometimes a different morphology for the nebula from that to be expected from the initial conditions. I consider how the different phases of ionization fronts and wind swept bubbles can be observationally distinguished.