The evolution of AGB stars towards planetary nebulae

We combined hydrodynamical simulations with stellar evolutionary calculations based on prescribed mass-loss rates in order to get a better understanding of how structure and kinematics of circumstellar matter develop with time during the late AGB and the following post-AGB evolution. We show (i) that the final density profile of the circumstellar shells produced by AGB mass loss falls off steeper than p similar to r(-2), (ii) that stages of high mass-loss rates are periodically interrupted by shorter phases of much lower outflow rates and speeds due to the luminosity dips associated with thermal pulses, and (iii) that during the post-AGB evolution ionization destroys the initial density and velocity distribution set up at the end of the AGB.