SPECTROPHOTOMETRY OF SOUTHERN PLANETARY-NEBULAE

Twenty-seven southern planetary nebulae of moderate to low surface bri ghtness have been observed in one or various positions across the nebu la with the 152 cm and the 3.6 m ESO telescopes equipped with the IDS (image dissector scanner) attached to Boller and Chivens spectrographs at spectral resolution between 8 and 13 Angstrom. The purpose was to search for objects chemically enriched in helium and nitrogen, accordi ng to the prediction of the stellar evolution theory of intermediate m ass stars. The chemical abundances of He, N, O, Ne, S and Ar have been determined in the individual positions, and averaged into values repr esentative of the whole nebulae. No cases of objects displaying chemic al gradients across the nebula have been detected. Eleven nebulae enri ched in helium and/or in nitrogen have been found, six of which detect ed as such for the first time. They are: A 37, A 70, Fg 1, MZ 1, MZ 2 and NGC 6578. They increase the number of the objects, which can be cl assified of type I of Peimbert.