Theoretical Orbital Period Distributions of Cataclysmic Variables above the Period Gap: Effects of Circumbinary Disks

Abstract

International audiencePopulation synthesis tools are used to investigate the population of nonmagnetic cataclysmic variables with unevolved main-sequence-like donors at orbital periods greater than 2.75 hr. In addition to the angular momentum losses associated with gravitational radiation, magnetic braking, and mass loss from the system, we also include the effects of circumbinary disks on the evolution. For a fractional mass input rate into the disk, corresponding to 3×10-4 of the mass transfer rate, the model systems exhibit a bounce at orbital periods greater than 2.75 hr. The simulations reveal that (1) some systems can exist as dwarf novae throughout their lifetime, (2) dwarf novae can evolve into novalike systems, and (3) novalike systems can evolve back into dwarf novae during their postbounce evolution to longer orbital periods. Among these subclasses, novalike cataclysmic variables would be the best candidates to search for circumbinary disks at wavelengths >~10 μm. The theoretical orbital period distribution is in reasonable accord with the combined population of dwarf novae and novalike systems above the period gap, suggesting the possibility that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model. The resulting population furthermore reveals the possible presence of systems with small mass ratios and a preference of O/Ne/Mg white dwarfs in dwarf nova systems in comparison to novalike systems. The novalike population furthermore shows a lack of systems with high-mass white dwarfs. The importance of observational bias in accounting for the differing populations is examined, and it is shown that an understanding of these effects is necessary in order to confront the theoretical distributions with the observed ones in a meaningful manner

Physical properties of IP Pegasi: an eclipsing dwarf nova with an unusually cool white dwarf

“…Some authors suggest alternatives, such as Willems et al (2007), who consider the effect of circumbinary discs on CV evolution. The theoretical orbital period distribution of Willems et al (2007) is a reasonable reproduction of the observed distribution, and they find that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model. In their model, different CVs can have very different long‐term s, and some systems can exist as dwarf novae throughout their lifetime.…”

Spatial distribution and galactic model parameters of cataclysmic variables

“…Therefore, even a rough estimate of space density may help to constrain the population models (Patterson, 1984). Standard models for the population of CVs predict a galactic space density of 10 −5 −10 −4 pc −3 (Ritter & Burkert, 1986;de Kool, 1992;Politano, 1996;Kolb, 2001;Willems et al, 2005Willems et al, , 2006. These predictions are inconsistent with the observed space densities of ∼10 −6 −10 −5 pc −3 (Warner, 1974;Patterson, 1984Patterson, , 1998Ringwald, 1993;Schwope et al, 2002;Aungwerojwit et al, 2005;Araujo-Betancor et al, 2005;Grindlay et al, 2005).…”

Degenerates with Dusty Disks: White Dwarfs and Cataclysmic Variables in the Infrared

“…In other cases (e.g., V592 Cas), the dust is in a circumbinary disk around the entire CV (Hoard et al 2009). Circumbinary disks were suggested as possible sources of additional angular momentum loss contributing to the secular evolution of CVs (Spruit & Taam 2001;Taam et al 2003;Willems et al 2005Willems et al , 2007; however, the Spitzer results imply total dust masses many orders of magnitude too small to be effective in that respect (Hoard et al 2009). Lingering questions about the dust remain: what is its composition, size, shape, etc.?…”