1994A&AS..107..481P

Twenty-seven southern planetary nebulae of moderate to low surface brightness have been observed in one or various positions across the nebula with the 152cm and the 3.6m ESO telescopes equipped with the IDS (image dissector scanner) attached to Boller & Chivens spectrographs at spectral resolution between 8 and 13A. The purpose was to search for objects chemically enriched in helium and nitrogen, according to the prediction of the stellar evolution theory of intermediate mass stars. The chemical abundances of He, N, O, Ne, S and Ar have been determined in the individual positions, and averaged into values representative of the whole nebulae. No cases of objects displaying chemical gradients across the nebula have been detected. Eleven nebulae enriched in helium and/or in nitrogen have been found, six of which detected 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 classified of type I of Peimbert.