Dredge-up effects in galactic and magellanic planetary nebulae^*

¹ Instituto Astronômico e Geofísico, Av. Miguel Stéfano 4200, 04301-904 São Paulo, Brazil
² Observatoire de la Côte d'Azur, BP. 4229, 06304 Nice Cedex 4, France

Send offprint request to: R.D.D. Costa

Received: 14 February 2000
Accepted: 29 June 2000

Abstract

Chemical abundances are reported for 23 planetary nebulae in the Small Magellanic Cloud. Average abundances agree with values found for HII regions, suggesting that progenitors of most of these objects have been formed in the last 1-2 Gyr. The N/O vs. O/H anticorrelation is confirmed for Magellanic and galactic planetaries, and a more robust result is obtained if objects of similar ages (or masses) are grouped together. For a given class, such a negative correlation suggests that the surface enrichment due to dredge-up episodes is more efficient at lower metallicities, in agreement with recent computations.