The hydrogen-depleted planetary nebulae Abell 30 and Abell 78.

Both Abell 30 and Abell 78 exhibit remarkable morphological disparities between their images with respect to the forbidden line of O III at 5007 A and the H-alpha line at 6563 A. This is due to hydrogen depletion in the inner regions of the two planetary nebulae. The material appears to be the end product of a hydrogen-burning shell which has subsequently been ejected. With the exception of helium and possibly carbon, the relative abundances of the other elements are, in general, normal. One of the knots in Abell 30, however, seems to be significantly deficient in oxygen and neon. The helium abundances relative to hydrogen are extremely high, with typical values by number of 6-10; these numbers show that hydrogen has been nearly completely converted to helium. The frequency of occurrence of planetary nebulae having helium-enriched shells of this type is discussed.