Poster abstract details

We report on our detailed study of the internal kinematics of round/elliptical double-shell planetary nebulae (PNe). Our new, quite enlarged sample of PNe covers all evolutionary phases across the Hertzsprung-Russell diagram. By means of high-resolution and high S/N spectrograms we determined bulk matter velocities of the wind-driven rims and the maximum (= post-shock) gas velocities of the thermally expanding shells. Our study confirms previously found results which were based on a much smaller sample of PNe: Both rim and shell accelerate with time, or evolution, but such that their difference velocities ($V_{\rm postshock} - V_{\rm rim}$) remain roughly constant. This finding is at variance with the commonly used assumption that PNe expand homologously (or uniformly), but in agreement with the prediction of radiation-hydrodynamics simulations if realistic initial conditions and time-evolution of stellar winds and radiation fields are considered.
We conclude that a typical PN is a dynamically active system throughout its entire life, controlled first by photo-ionisation and later also by wind interaction.