Detailed nucleosynthesis in the ejecta of classical novae has been determined for a grid of hydrodynamic nova models. The reported 14 evolutionary sequences, followed from the onset of accretion up to the explosion and ejection stages, span a range of CO and ONe white dwarf masses (0.8-1.35 M ⊙ ) and mixing levels between the accreted envelope and the underlying white dwarf core (25-75%). The synthesis of each isotope, from 1 H to 40 Ca, is discussed along with its sensitivity to model parameters. Special emphasis is given to isotopes such as 13 C, 15 N, and 17 O, which may account for a significant fraction of their Galactic content. Production of the radioactive isotopes 7 Be, 22 Na, and 26 Al is also analyzed, since they may provide a direct test of the thermonuclear runaway model through their γ-ray emission. The resulting elemental yields reproduce fairly well the spectroscopic abundance determinations of several well studied classical novae.

White dwarfs are the remnants of stars of low and intermediate masses on the main sequence. Since they have exhausted all of their nuclear fuel, their evolution is just a gravothermal process. The release of energy only depends on the detailed internal structure and chemical composition and on the properties of the envelope equation of state and opacity ; its consequences on the cooling curve (i.e., the luminosity vs. time relationship) depend on the luminosity at which this energy is released.The internal chemical proÐle depends on the rate of the 12C(a, c)16O reaction as well as on the treatment of convection. High reaction rates produce white dwarfs with oxygen-rich cores surrounded by carbon-rich mantles. This reduces the available gravothermal energy and decreases the lifetime of white dwarfs.In this paper we compute detailed evolutionary models providing chemical proÐles for white dwarfs having progenitors in the mass range from 1.0 to 7 and we examine the inÑuence of such proÐles in M _ , the cooling process. The inÑuence of the process of separation of carbon and oxygen during crystallization is decreased as a consequence of the initial stratiÐcation, but it is still important and cannot be neglected. As an example, the best Ðt to the luminosity functions of Liebert et al. and Oswalt et al. gives an age of the disk of 9.3 and 11.0 Gyr, respectively, when this e †ect is taken into account, and only 8.3 and 10.0 Gyr when it is neglected.

Infrared and ultraviolet observations of nova light curves have confirmed grain formation in their expanding shells that are ejected into the interstellar medium by a thermonuclear runaway. In this paper, we present isotopic ratios of intermediate-mass elements up to silicon for the ejecta of CO and ONe novae, based on 20 hydrodynamic models of nova explosions. These theoretical estimates will help to properly identify nova grains in primitive meteorites. In addition, equilibrium condensation calculations are used to predict the types of grains that can be expected in the nova ejecta, providing some hints on the puzzling formation of C-rich dust in O>C environments. These results show that SiC grains can condense in ONe novae, in concert with an inferred (ONe) nova origin for several presolar SiC grains.Comment: 42 pages. Accepted for publication in The Astrophysical Journa

We report the discovery of five SiC grains and one graphite grain isolated from the Murchison carbonaceous meteorite whose major-element isotopic compositions indicate an origin in nova explosions. The grains are characterized by low 12C/13C (4-9) and 14N/15N (5-20) ratios, large excesses in 30Si (30Si/28Si ratios range to 2.1 times solar) and high 26Al/27Al ratios. These isotopic signatures are theoretically predicted for the ejecta from ONe novae and cannot be matched by any other stellar sources. Previous studies of presolar grains from primitive meteorites have shown that the vast majority formed in red giant outflows and supernova ejecta. Although a classical nova origin was suggested for a few presolar graphite grains on the basis of 22Ne enrichments, this identification is somewhat ambiguous since it is based only on one trace element. Our present study presents the first evidence for nova grains on the basis of major element isotopic compositions of single grains. We also present the results of nucleosynthetic calculations of classical nova models and compare the predicted isotopic ratios with those of the grains. The comparison points toward massive ONe novae if the ejecta are mixed with material of close-to-solar composition.Comment: 20 pages, 5 figures, 1 table. ApJ, in pres