SIMBAD references

In a sample of 94 planetary nebulae of the Galactic disk we find a systematic decrease of the abundances of He, N, O, S, and Ar with height above the Galactic plane, and also with radial velocity. Over an interval of 3kpc the abundance of O, S, and Ar decrease by 0.1 ... 0.2dex. This value is in good agreement with the predictions of an empirical model for the chemical and kinematical evolution of the disk, based on relations and constraints of the solar neighbourhood. The radial migration of the progenitor stars, caused by the velocity dispersion increasing with age, is found to be quite important for the vertical metallicity profile.