Formation and Evolution of Accreting Compact Objects

Belloni, Diogo; Schreiber, M. R.

doi:10.1007/978-981-16-4544-0_98-1

Cited by 3 publications

(1 citation statement)

References 306 publications

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“…According to the standard theory for the formation and evolution of cataclysmic variables (CVs, Belloni & Schreiber 2023;Knigge et al 2011), and independent of the details of simulating CV evolution, a large number of all CVs should already have passed the period minimum, that is, the population of CVs should be dominated by systems evolving toward longer orbital periods consisting of a cool white dwarf with a brown dwarf companion. The predicted fraction of these so-called period bouncers among CVs was estimated decades ago to be 70% (Kolb 1993), a value roughly in agreement with more recent calculations, which predict 38−60% (Goliasch & Nelson 2015) and ∼75% (Belloni et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Period bouncers as detached magnetic cataclysmic variables

Schreiber,

Belloni,

van Roestel

2023

A&A

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Context. The general prediction that more than half of all cataclysmic variables (CVs) have evolved past the period minimum is in strong disagreement with observational surveys, which show that the relative number of these objects is just a few percent. Aims. Here, we investigate whether a large number of post-period minimum CVs could detach because of the appearance of a strong white dwarf magnetic field potentially generated by a rotation- and crystallization-driven dynamo. Methods. We used the MESA code to calculate evolutionary tracks of CVs incorporating the spin evolution and cooling as well as compressional heating of the white dwarf. If the conditions for the dynamo were met, we assumed that the emerging magnetic field of the white dwarf connects to that of the companion star and incorporated the corresponding synchronization torque, which transfers spin angular momentum to the orbit. Results. We find that for CVs with donor masses exceeding ∼0.04 M⊙, magnetic fields are generated mostly if the white dwarfs start to crystallize before the onset of mass transfer. It is possible that a few white dwarf magnetic fields are generated in the period gap. For the remaining CVs, the conditions for the dynamo to work are met beyond the period minimum, when the accretion rate decreased significantly. Synchronization torques cause these systems to detach for several gigayears even if the magnetic field strength of the white dwarf is just one MG. Conclusions. If the rotation- and crystallization-driven dynamo – which is currently the only mechanism that can explain several observational facts related to magnetism in CVs and their progenitors – or a similar temperature-dependent mechanism is responsible for the generation of magnetic field in white dwarfs, most CVs that have evolved beyond the period minimum must detach for several gigayears at some point. This reduces the predicted number of semi-detached period bouncers by up to ∼60 − 80%.

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Section: Introductionmentioning

confidence: 99%

Period bouncers as detached magnetic cataclysmic variables

Schreiber,

Belloni,

van Roestel

2023

A&A

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Reversing the verdict: Cataclysmic variables could be the dominant progenitors of AM CVn binaries after all

Belloni,

Schreiber

2023

A&A

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Context. AM CVn binaries are potential progenitors of thermonuclear supernovae and strong sources of persistent gravitational wave radiation. For a long time, it has been believed that these systems cannot descend from cataclysmic variables (CVs), at least not in large numbers, because the initial conditions need to be fine-tuned and, even worse, the resulting surface hydrogen abundance would be high enough to be detected which contradicts a defining feature of AM CVn binaries. Aims. Here we show that both claimed weaknesses of the CV formation channel for AM CVn binaries are model-dependent and rely on poorly constrained assumptions for magnetic braking. Methods. We performed binary evolution simulations with the MESA code for different combinations of post-common-envelope white dwarf and companion masses as well as orbital periods assuming the CARB model for strong magnetic braking. Results. We found that AM CVn binaries with extremely-low surface hydrogen abundances are one natural outcome of CV evolution if the donor star has developed a non-negligible helium core prior to the onset of mass transfer. In this case, after hydrogen envelope exhaustion during CV evolution, the donor becomes degenerate and its surface hydrogen abundance substantially drops and becomes undetectable. Our simulations also show that the CV formation channel is able to explain the observed AM CVn binaries with very low mass and bloated donor stars (Gaia14aae and ZTF J1637+49). Conclusions. CVs with evolved donors are likely the progenitors of at least a fraction of AM CVn binaries.

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Gravitational wave forms of galactic compact binaries with mass-transfer correction

Zhang,

Liu,

et al. 2024

Phys. Rev. D

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Formation and Evolution of Accreting Compact Objects

Cited by 3 publications

References 306 publications

Period bouncers as detached magnetic cataclysmic variables

Period bouncers as detached magnetic cataclysmic variables

Reversing the verdict: Cataclysmic variables could be the dominant progenitors of AM CVn binaries after all

Gravitational wave forms of galactic compact binaries with mass-transfer correction

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