On the reliability of planetary nebulae as extragalactic probes

We report on the first 1D radiation-hydrodynamics simulations aimed at exploring the metallicity dependance of the evolution of planetary nebulae. Using scaled mean abundances, based on Galactic disk objects, we found that for lower metallicities the nebulae become more dilute and prone to departures from thermal equilibrium because of the reduced wind power of the central star and the reduced cooling efficiency of the nebular gas. At selected evolutionary phases we 'switched off' the hydrodynamic terms and Computed equilibrium models for the fixed density structure and radiation field. This enabled us to study how the electron temperature and the emission of important diagnostic lines is influenced by hydrodynamics.