Cataclysmic variables with evolved secondaries and the progenitors of AM CVn stars

By P. Podsiadlowski, Zhanwen Han, S. Rappaport. 2001

144 citations recorded by the source corpus.

We present the results of a systematic study of cataclysmic variables (CVs) and related systems, combining detailed binary-population synthesis (BPS) models with a grid of 120 binary evolution sequences calculated with a Henyey-type stellar evolution code. In these sequences, we used three masses for the white dwarf (0.6, 0.8 and 1.0 M-circle dot) and seven masses for the donor star in the range of 0.6-1.4 M-circle dot . The shortest orbital periods were chosen to have initially unevolved secondaries, and the longest orbital period for each secondary mass was taken to be just longer than the bifurcation period (16-22 h), beyond which systems evolve towards long orbital periods. These calculations show that systems that start with evolved secondaries near the end or just after their main-sequence phase become ultracompact systems with periods as short as similar to7 min. These systems are excellent candidates for AM Canum Venaticorum (AM CVn) stars. Using a standard BPS code, we show how the properties of CVs at the beginning of mass transfer depend on the efficiency for common-envelope (CE) ejection and the efficiency of magnetic braking. In our standard model, where CE ejection is efficient, some 10 per cent of all CVs have initially evolved secondaries (with a central hydrogen abundance X-c<0.4) and ultimately become ultracompact systems (implying a Galactic birth rate for AM CVn-like stars of similar to10(-3) yr(-1)). While these systems do not experience a period gap between 2 and 3 h, their presence in the gap does not destroy its distinct appearance. Almost all CVs with orbital periods longer than similar to5 h are found to have initially evolved or relatively massive secondaries. Based on a preliminary analysis, we find that their distribution of effective temperatures appears to be in reasonably good agreement with the distribution of spectral types obtained by Beuermann et al.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/264f4e0ce9ed7a3d23b6c56597f2994b0f318a4f

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In Astronomy and Astrophysics

Citations in the corpus

Short-period AM CVn systems as optical, X-ray and gravitational-wave sources (2003, methodology): “Taking this time as typical, and assuming a birth rate of 6.4 × 10−5 yr−1 for systems evolving to P < 25 min, as in the standard model of Podsiadlowski et al. (2003), we expect 2400 post-CV ultracompact systems in the Galaxy, compared to the 140 000 from the channels discussed here.”
Mass-Radius Relationships for Solid Exoplanets (2007, background): “…an AM CVn (AM Canes Venatici), composed of two very Hpoor white dwarfs (i.e., He core white dwarfs) surrounded by a circumbinary helium accretion disk formed during mass transfer from the less massive to the more massive white dwarf (see, e.g., Podsiadlowski et al. (2003), and references therein).”
THE EVOLUTION OF CATACLYSMIC VARIABLES AS REVEALED BY THEIR DONOR STARS (2011, background): “This may seem like a poor approximation, but Podsiadlowski et al. (2003) have shown that significantly evolved donors (with central hydrogen fractions of Xc < 0.4) only begin to dominate the CV population above periods of 5 hr.”