Abstract
Photoelectric spectrophotometry of emission lines in the 3400-7400 A region for the planetary nebula 108-76 deg 1 (BB1) is presented. These observations are then used to derive the relative abundances of H, He, C, N, O, and Ne. The abundances of the halo PN (BB1, H4-1 and K648) are compared with those predicted by stellar evolution theory under the assumption that the envelope has the chemical composition of the matter located between the H burning shell and the surface. The observed He/H and C/O values are found to be higher than predicted, implying that the halo PN contains matter from deeper layers than the H burning shell. Moreover, the O/Ar, N/Ar and Ne/Ar values in the halo are higher than in the solar neighborhood, and at least part of this enrichment is produced by the PN progenitors.
