THE COMPOSITION OF NOVA EJECTA FROM MULTICYCLE EVOLUTION MODELS

Following a previous systematic study involving calculations of evolut ionary sequences of nova outbursts through several cycles, for combina tions of parameters-the accreting white dwarf (WD's) mass, its core te mperature, and the mass transfer rate-spanning the entire parameter sp ace, assuming CO WDs (with C and O in equal mass fractions), we now co nsider the detailed composition of the ejecta for the subset of models which simulated classical nova outburst. We also investigate the effe ct of the additional input parameter-the WD composition-on nova charac teristics by calculating evolutionary sequences with pure-carbon and p ure-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 m ost of the observed abundances and abundance ratios, and that correlat ions between them, if any, are in very good agreement with observation s. The WD composition is generally not reflected in the abundances of the ejecta: whereas a large fraction of the carbon is always turned in to nitrogen, oxygen is in some cases unaffected and in others almost c ompletely destroyed. Hence ejecta abundances cannot be used to deduce the WD composition. Ejected masses of pure O WD progenitors exceed tho se of CO progenitors, sometimes by a factor of 4. The isotopes C-13 an d O-17 are in all cases significantly overabundant, compared to the so lar composition: C-12/C-13 varies between 0.97 and 3.8 (by number) and O-16/O-17 varies between 1.8 and 55; N-15, however, is sometimes grea tly enhanced and sometimes underabundant, N-14/N-15 varying over a ver y wide range, from 2.4 to 33,000.