Cataclysmic variable star

Abstract: This paper is a sequel to an earlier paper devoted to multiple, multicycle nova evolution models (Prialnik & Kovetz, Paper I), which showed that the different characteristics of nova outbursts can be reproduced by varying the values of three basic and independent parameters: the white dwarf mass, MWD, the temperature of its isothermal core, TWD, and the mass transfer rate, . Here we show that the parameter space is constrained by several analytical considerations and find its limiting surfaces. Consequently, we extend the grid of multicycle nova evolution models presented in Paper I to its limits, adding multicycle nova outburst calculations for a considerable number of new parameter combinations. In particular, the extended parameter space that produces nova eruptions includes low mass transfer rates down to 5 × 10-13 M☉ yr-1 and more models for low TWD. Resulting characteristics of these runs are added to the former parameter combination results to provide a full grid spanning the entire parameter space for carbon-oxygen white dwarfs. The full grid covers the entire range of observed nova characteristics, even those of peculiar objects, which have not been numerically reproduced until now. Most remarkably, runs for very low lead to very high values for some characteristics, such as outburst amplitude A 20, high super-Eddington luminosities at maximum, heavy element abundance of the ejecta Zej ≈ 0.63, and high ejected masses mej ≈ 7 × 10-4 M☉.

Abstract: We present an observational study of the structure and evolution of cataclysmic and low-mass X-ray binaries, concentrating on the 124 systems for which orbital periods are known. The eruptive properties and mass transfer rates of these stars are found to be highly correlated wit their orbital periods, suggesting that both the eruptive activity and the long-term evolution are determined by the properties of the lobe-filling secondaries. The secondaries do not satisfy the commonly used theoretical models of low-mass zero-age main-sequence (ZAMS) stars, but are, in general consistent with the empirically derived properties of the lower main sequence. We show stars, that R/R/sub direct-sum/ = (M/M/sub direct-sum/)/sup 0.88/ for low-mass ZAMS stars in the field, in wide binaries and in cataclysmic binaries. For masses above 0.8 M/sub direct-sum/, the empirical ZAMS is in reasonable agreement with the models. But in this regime (corresponding to orbital periods > or approx. = 9 hr), the secondaries in cataclysmic binaries are found to be slightly evolved from ZAMS.

Abstract: X rays emitted in the inner part of an accretion disk system can heat the surface of the disk farther out, producing a corona and possibly driving off a strong wind. The dynamics of Compton-heated coronae and winds are analyzed using an approximate two-dimensional technique to estimate the mass loss rate as a function of distance from the source of X rays. The findings have important dynamical implications for accretion disks in quasars, active galactic nuclei, X ray binaries, and cataclysmic variables. These include: mass loss from the disk possibly comparable with or exceeding the net accretion rate onto the central compact object, which may lead to unstable accretion; sufficient angular momentum loss in some cases to truncate the disk in a semidetached binary at a smaller radius than that predicted by tidal truncation theories; and combined static plus ram pressure in the wind adequate to confine line-emitting clouds in quasars and Seyfert galaxies.

Abstract: 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 1H to 40Ca is discussed, along with its sensitivity to model parameters. Special emphasis is placed on isotopes such as 13C,15N, and 17O, whose synthesis may account for a significant fraction of their Galactic content. Production of the radioactive isotopes 7Be,22Na, and 26Al 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 the spectroscopic abundance determinations of several well-studied classical novae fairly well.