The Composition of Nova Ejecta from Multicycle Evolution Models

Abstract

Following a previous systematic study involving calculations of evolutionary sequences of nova outbursts through several cycles, for combinations of parameters---the accreting white dwarf (WD's) mass, its core temperature, and the mass transfer rate---spanning the entire parameter space, assuming CO WDs (with C and O in equal mass fractions), we now consider the detailed composition of the ejecta for the subset of models which simulated classical nova outburst. We also investigate the effect of the additional input parameter---the WD composition---on nova characteristics by calculating evolutionary sequences with pure-carbon and pure-oxygen WD progenitors. The stellar evolution code used includes an extended nuclear reactions network, OPAL opacities, and diffusion of all elements. Our main conclusions are that CO progenitors reproduce most of the observed abundances and abundance ratios, and that correlations between them, if any, are in very good agreement with observations. The WD composition is generally not reflected in the abundances of the ejecta: whereas a large fraction of the carbon is always turned into nitrogen, oxygen is in some cases unaffected and in others almost completely destroyed. Hence ejecta abundances cannot be used to deduce the WD composition. Ejected masses of pure O WD progenitors exceed those of CO progenitors, sometimes by a factor of 4. The isotopes 13C and 17O are in all cases significantly overabundant, compared to the solar composition: 12C/13C varies between 0.97 and 3.8 (by number) and 16O/17O varies between 1.8 and 55; 15N, however, is sometimes greatly enhanced and sometimes underabundant, 14N/15N varying over a very wide range, from 2.4 to 33,000.