A modest change in magnetic braking at the fully convective boundary explains cataclysmic variable evolution
arXiv:2603.14560 · doi:10.1051/0004-6361/202659326
Abstract
Context. For decades, reproducing the orbital period distribution of non-magnetic Cataclysmic Variables (CVs) seemed to require a drastic decrease, usually termed disruption, of angular momentum loss through magnetic braking at the fully convective boundary, which argued for a change in the dynamo mechanism operating in fully and partially convective stars. However, recent studies showed that the magnetic braking prescription traditionally used in CV evolution theory is clearly outdated as saturation, that is, a weak period dependence for rapidly rotating stars, is not included. Aims. Here we test an updated version of a saturated magnetic braking prescription that has been developed to explain the spin-down of single stars in the context of CV evolution. This prescription contains a boosting and a disruption parameter that represent the change in the strength of magnetic braking at the fully convective boundary. Methods. We performed state of the art MESA simulations for CVs with the revised saturated magnetic braking prescription. Results. As in previous studies, we found that magnetic braking needs to be stronger in close binaries than in single stars and that, in contrast to what is observed in single stars, magnetic braking needs to be reduced at the fully convective boundary. However, in contrast to previous studies of CV evolution, only a moderate disruption by a factor of 2 - 3 is sufficient to explain key features of the CV orbital period distribution and the measured mass-radius relation for CV donors. Conclusions. The relatively small decrease of the efficiency of magnetic braking at the fully convective boundary might have implications for our understanding of dynamo models for fully and partially convective stars.
Accepted for publication in A&A
References in corpus (16)
- Modules for Experiments in Stellar Astrophysics (MESA)
- Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
- The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
- The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law
- A Temporary Epoch of Stalled Spin-Down for Low-Mass Stars: Insights from NGC 6811 with Gaia and Kepler
- Relation of X-ray activity and rotation in M dwarfs and predicted time-evolution of the X-ray luminosity
- Flare Rates, Rotation Periods. and Spectroscopic Activity Indicators of a Volume-Complete Sample of Mid-to-Late M dwarfs within 15 Parsecs
- The evolutionary status of Cataclysmic Variables: Eclipse modelling of 15 systems
- Evidence for reduced magnetic braking in polars from binary population models
- Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF
- The cataclysmic variable orbital period gap: More evident than ever
- Characterising eclipsing white dwarf M dwarf binaries from multi-band eclipse photometry
- Rossby numbers of fully and partially convective stars
- Rotation at the Fully Convective Boundary: Insights from Wide WD + MS Binary Systems
- Further evidence of saturated, boosted, and disrupted magnetic braking from evolutionary tracks of cataclysmic variables
- Estimating the Convective Turnover Time