AN EXTENDED GRID OF MULTICYCLE NOVA EVOLUTION MODELS

According to the nova theory, observed characteristics of novae may be reproduced by varying the values of three basic and independent param eters: the accreting white dwarf's mass M(WD), its temperature T-WD, a nd the mass transfer rate M. Calculations performed to date have, howe ver, left wide regions of the parameter space unexplored. We carry out a systematic study involving calculations of evolutionary sequences o f nova outbursts through several cycles, for 64 parameter combinations spanning the entire parameter space, assuming CO white dwarfs (WDs). An updated stellar evolution code is used, including an extended nucle ar reactions network, new opacities (OPAL), diffusion of all elements and the effect of radiation pressure on mass loss. We find that the en tire range of observed nova characteristics can be accounted for, incl uding recurrent and symbiotic novae. Recurrent novae may be obtained o n relatively low-mass WDs (similar to 1 M(.)). Accretion at rates M gr eater than or equal to 10(-7) M(.) yr(-1) invariably results in an inc rease of M(WD) and may, eventually, lead to a type Ia supernova. For a ccretion rates M less than or equal to 10(-9) M(.) yr(-1), M(WD) decre ases under all circumstances. The overall dependence of nova character istics on the basic parameters is analyzed. Observed correlations betw een nova properties, as well as the conspicuous lack of correlation be tween other properties, are verified by the theoretical results. Among all the observed properties of novae there are three that appear to b e independent of each other: the time of decline by 3 magnitudes t(3), the heavy element abundance of the ejecta Z(ej), and their helium con tent Y-ej. Our calculations yield t(3)(M(WD), T-WD, M), Z(ej)(M(WD), T -WD, M), Y-ej(M(WD), T-WD, M) at discrete points over the entire param eter space. By matching observed characteristics of a particular nova with calculated counterparts, it is possible to derive the WD's mass a nd temperature and the (average) accretion rate as well as additional observable properties. We find an excellent match for the measured exp ansion velocities, but the calculated ejected masses are generally sma ller than those estimated from observations.