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

This paper presents a homogeneous study of abundances in a sample of 79northern galactic planetary nebulae whose morphological classes have beenuniformly determined. Ionic abundances and plasma diagnostics were derived fromselected optical line strengths in the literature, and elemental abundanceswere estimated with the Ionization Correction Factor developed by Kingsbourgh &Barlow (1994). We compare the elemental abundances to the final yields obtainedfrom stellar evolution models of low-and intermediate-mass stars, and weconfirm that most Bipolar planetary nebulae have high nitrogen and heliumabundance, and are the likely progeny of stars with main-sequence mass largerthan 3 solar masses. We derive =0.27, and discuss the implication of sucha high ratio in connection with the solar neon abundance. We determine thegalactic gradients of oxygen and neon, and found Delta log (O/H)/Delta R=-0.01dex/kpc$ and Delta log (Ne/H)/Delta R=-0.01 dex/kpc. These flat PN gradients donot reconcile with galactic metallicity gradients flattening with time.Comment: The Astrophysical Journal, in pres