The halo planetary nebulae M2-29 and BB-1

Extract

The physical conditions and chemical abundances were determined for M2-29 and BB-1 from optical spectrophotometric data and from available IUE material (Table 1). M2-29 has the lowest O/H ratio in PNe and it belongs to the Ar and S rich type IV PN group while BB-1 is very C, N, and Ne rich being Ar and S poor. Comparing with all known PNe of type IV it is found that C/N/O/Ne/Ar do not vary in lockstep, but C, N, O and Ne appear enriched in Ar poor objects (Table 2). C and N are expected to be enriched by the central star, however the anomalous O/Ne/Ar behavior is not understood unless O and Ne are also enriched by the progenitor star. The paper in full will appear in P.A.S.P. 1991.