ON THE INTERPRETATION AND IMPLICATIONS OF NOVA ABUNDANCES - AN ABUNDANCE OF RICHES OR AN OVERABUNDANCE OF ENRICHMENTS

We reexamine the question of the frequency of occurrence of oxygen-neon-magnesium (ONeMg) degenerate dwarfs in classical nova systems, in light of recent observations which have been interpreted as suggesting that ''neon novae'' can be associated with relatively low mass white dwarfs. Determinations of heavy-element concentrations in nova ejecta are reviewed, and possible interpretations of their origin are examined. We conclude that, of the 18 classical novae for which detailed abundance analyses are available, only two (or possibly three) seem unambiguously to demand the presence of an underlying ONeMg white dwarf: V693 CrA 1981, V1370 Aql 1982, and possibly QU Vul 1984. Three other novae which exhibit significant neon enrichments, relative to their total heavy-element concentrations, are RR Pic 1925, V977 Sco 1989, and LMC 1990 No. 1. This result is entirely consistent with present frequency estimates, and our interpretation of the lower levels of enrichment in other systems explains, in a natural way, the existence of relatively low mass white dwarfs in some of the ''neon'' novae.