Ultrashort-Period Binaries. II. HZ 29 (=AM CVn): a Double-White Semidetached Postcataclysmic Nova?

NLTE accretion disc models for the AM Canum Venaticorum systems

“…Since the interacting binary model was first proposed by Faulkner et al (1972), many studies of the evolution and stability of these system have taken place. It is now commonly agreed that the orbital period will increase with time due to mass transfer, which again will decrease with time.…”

“…Five years later, photometric variability with a period of 17.5 min was discovered; Smak (1967) and Paczyński (1967) suggested that it could be a semi-detached pair of degenerate objects in which mass transfer is driven by loss of angular momentum due to gravitational wave radiation. Flickering, which is typical for cataclysmic variables, was found by Warner & Robinson (1972), and this inspired Faulkner, Flannery & Warner (1972) to propose the double-degenerate white dwarf model, which has been the main accepted explanation for the AM CVn systems since then. The dominant photometric period is 525 s, which is a first harmonic of the fundamental period of 1051 s .…”

“…At present, we know of eight such systems: AM CVn, CR Boo, HP Lib, V803 Cen, CP Eri , GP Com, RX J1914.4+245, and KL Dra (Nelemans et al 2001a). It is currently believed that they are interacting binary white dwarf systems (Faulkner et al 1972) with a degenerate C-O primary in which the secondary low mass object is semi-degenerate with M 2 ≤ 0.084 M and is slowly losing mass as it is layer by layer wrapped off in a process transferring an almost a pure helium gas to the white dwarf primary, most likely in the equatorial region in which a helium accretion disc is formed.…”

Gravitational Radiation and the Evolution of Low Mass Binaries

“…Taam and I have recently shown (Taam and Faulkner, 1975) that such a rate of accretion will initiate a thermonuclear runaway in the envelope of a 1M® white dwarf. In earlier studies Giannone and Weigert (1967), using rates of 10" It seems to me that the analysis of Bath etal. (1974), applied consistently to Warner's observations, essentially rules out the very mechanism they claim it supports.…”

“…This has been examined in several contexts (e.g. Paczynski, 1967;Faulkner, 1971;Faulkner et al, 1972). The timescale Tis still largely appropriate, but the precise behaviour depends upon the slopes of the log R-\og M relationships for the secondary star (n) and the Roche lobe as a geometrical entity (a) in addition to the mass fraction (//=Af2/(^1 +^2)) present in the secondary.…”