Radiation gasdynamics of planetary nebulae – VI. The evolution of aspherical planetary nebulae

This paper reports the results of the numerical study of the formation ofaspherical Planetary Nebulae through the Generalised Interacting Winds Model,taking into account the effects caused by the evolving central star and fastwind. The results show for the first time that aspherical nebulae do formwithin the required time scale. Consideration of the development of the nebulashows that in the early stages it is the ionization of the aspherical AGB windthat contributes considerably to the shaping of the nebula. Furthermore thepassing through of the ionization front may modifies the density distributionin the slow wind, leading to the formation of a surrounding envelope, andsometimes a different morphology for the nebula than was to be expected fromthe initial conditions. I consider how the different phases of ionizationfronts and wind swept bubbles can be observationally distinguished.