NUCLEOSYNTHESIS IN CLASSICAL NOVAE AND ITS CONTRIBUTION TO THE INTERSTELLAR-MEDIUM

Classical novae, explosions that result from thermonuclear runaways (T NRs) on the surfaces of white dwarfs (WDs) accreting hydrogen-rich mat ter in close binary systems, are sporadically injecting material proce ssed by explosive hydrogen-burning nucleosynthesis into the interstell ar medium (ISM). Although novae probably have processed less than simi lar to 0.3% of the interstellar matter in the Galaxy, both theoretical and observational evidence suggests that they may be important source s of the nuclides Li-7, N-15, and O-17, as well as the radioactive iso topes Na-22 and Al-26. The latter nuclides are astrophysically importa nt in that they may have been involved in the production of the Ne-22 (Ne-E) and Mg-26 enrichments identified in meteoritic inclusions, the composition of which is thought to be representative of the chemical a nd mineral contents of the primitive solar nebula. These inclusions ma y be partially composed of dust condensed in nova outbursts. We review theoretical expectations for the yields of various isotopes in nova o utbursts and conclude that any of the heavy isotope anomalies attribut able to novae are most likely produced by the approximately 25%-33% of novae that occur in systems containing massive (M- > 1.2 M.) oxygen- neon-magnesium (ONeMg) WDs. We attempt to place quantitative constrain ts on the degree to which classical novae participate in the productio n of chemical anomalies, both in the primitive solar system and on a G alactic scale, Diffuse Galactic gamma-ray fluxes provide particularly important clues to and constraints on the Na-22 and Al-26 yields from novae. Ultraviolet (UV), optical, and infrared (IR) emission-line spec tra of classical novae reveal the abundances of some of the gas-phase elements present in the ejecta; recent results are reviewed. We descri be how IR observations of novae reveal dust formation and gas-phase li ne emission and how they distinguish the temporal development of nova explosions on carbon-oxygen (GO) WDs (CO novae) from those on ONeMg WD s (ONeMg or ''neon'' novae). Recent studies show that the ejecta in so me novae can be strongly cooled by near-and mid-IR forbidden-line radi ation from highly ionized (''coronal'') atomic states. We compare the abundances deduced from recent UV, optical, and IR observations with t heoretical predictions, and we suggest that future studies of IR coron al emission lines may provide additional key information. Novae produc e only about 0.1% of the Galactic ''stardust'' (dust condensed in stel lar outflows), but IR observations show that it may be some of the mor e interesting dust. Novae appear capable of producing astrophysical du st of virtually every known chemical and mineral composition. We summa rize recent IR observations of the dust production scenario in novae a nd argue that neon novae may lead to the formation of dust grains that carry the Ne-E and Mg-26 anomalies.