Evolution of aspherical

This paper reports the results of the numerical study of the formation of aspherical Planetary Nebulae through the Generalised Interacting Winds Model, taking into account the eeects caused by the evolving central star and fast wind. The results show for the rst time that aspherical nebulae do form within the required time scale. Consideration of the development of the nebula shows that in the early stages it is the ionization of the aspherical AGB wind that contributes considerably to the shaping of the nebula. Furthermore the passing through of the ionization front may modiies the density distribution in the slow wind, leading to the formation of a surrounding envelope, and sometimes a diierent morphology for the nebula than was to be expected from the initial conditions. I consider how the diierent phases of ionization fronts and wind swept bubbles can be observationally distinguished.