Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way

Abstract

This paper presents a homogeneous study of abundances in a sampleof 79 northern Galactic planetary nebulae (PNe) whose morphologicalclasses have been uniformly determined. Ionic abundances and plasmadiagnostics were derived from selected optical line strengths inthe literature, and elemental abundances were estimated with theionization correction factor developed by Kingsbourgh & Barlow in1994. We compare the elemental abundances to the final yields obtainedfrom stellar evolution models of low- and intermediate-mass stars,and we confirm that most bipolar PNe have high nitrogen and heliumabundance and are the likely progeny of stars with main-sequencemass greater than 3 M-circle dot. We derive = 0.27 and discussthe implication of such a high ratio in connection with the solarneon abundance. We determine the Galactic gradients of oxygen andneon found Delta log (O/H)/Delta R = -0.01 dex kpc(-1) and Deltalog (Ne/H)/Delta R = -0.01 dex kpc(-1). These flat PN gradients areirreconcilable with Galactic metallicity gradients flattening withtime.