Chemical Abundances In Nova Ejecta

Nova outbursts are the results of thermonuclear runaways (TNRs) of rich hydrogen on the surfaces of white dwarfs (WDs) accreting hydrogen matter in the close binary sys-tems. As a consequence, a significant fraction of material, enriched in the products of hot hydrogen burning, is ejected into the interstellar medium (ISM). The ejected matter enrich and change the chemical abundances of the surrounding environment, thereby af-fecting the generation, enrichment and distribution of the chemical elements in the ISM. Both observational and theoretical evidences imply that novae may be the major sources of the odd-numbered nuclei 13C,15N and 17O, and novae clearly contribute to the chemi-cal element evolution of the Galaxy. Understanding novae and analyzing the enrichments of chemical elements in the ejected materials are the key factors for understanding the chemical evolution of galaxy and are very interested and excited.According to the nova outbursts model from Yaron et al.(2005) and Jose et al.(1998), we follow the evolutions of both components with the rapid BSE code, including the effect of tides on binary evolution, then calculate the chemical abundances of all the elements. Here, for purpose of investigating the Galactic occurrence rate of novae and the contri-bution of chemical abundances in nova ejecta to the ISM of the Galaxy, we perform a population synthesis method for a sample of 106 binary systems. We also plot and present the final abundances of the chemical elements in the nova ejecta, and continue with a discussion of the observation and simulation results.In our work, we find that the occurrence rate of CNe in the Galaxy is about 54yr-1, and find that the ejected mass by classical novae (CNe) is about 2.7×103 M(?) yr-1. In the nova ejecta, the contributions of C, N and O elements to the ISM in the Galaxy are about 9.1 × 1(T7M(?) yv-1 7.3 × 10-6 M(?) yr-1 and 7.1 × 10-6 M(?) yr-1, respectively. Hence, the average ejected mass of 13C by novae is 3.2 × 107 M(?) yr-1, the average yields of isotopes 15N and 17O are 1.1 × 10-8 Mo yr-1 and 2.8 × 107 Mo yr-1, respectively. We can also estimate that about 10%,5% and 20% of 13C,15N and 17O in the ISM of the Galaxy come from nova ejecta, respectively.In short, although the overall mass contribution to the ISM produced by novae is little, novae are the main sources of the odd-numbered nuclei 13C,15N and 17O in the ISM. The isotopic ratios of C, N and O, that is,13C/12C,15N/14N and 17O/16O, are higher about one order of magnitude than those in red giants. Such nuclei differ markedly from solar, and they are difficult to form in other astrophysical hosts. Unfortunately, the chemical abundances of C, N and O calculated by our model can not cover all of observational values. This means that there is still a long way to go in terms of understanding novae.