Abundances in Magellanic Cloud planetary nebulae

Abstract

The enhanced nitrogen abundances in planetary nebulae (PN) show the effects of CN-cycle processing at the time of the first dredge-up, while their very enhanced carbon abundances show the effects of the third dredge-up. The efficiency of both the first and third dredge-ups increases with decreasing initial metallicity. ON-cycle depletion of oxygen via the second dredge-up does not appear to have been significant in LMC Type I planetary nebulae (those with N/O > 0.5) – these nebulae have experienced the third dredge-up and envelope-burning, giving enhanced C+N abundances. The LMC Type I PN show enhanced Ne/O ratios. Enrichment rates in nitrogen and carbon by PN are estimated for the ISM s of the Magellanic Clouds.