Mechanisms for magnetic braking boost and disruption: the role of irradiation-driven winds and convective turnover time spike in cataclysmic variables

Abstract

The saturated, boosted, and disrupted magnetic braking (SBD MB) model is an empirical prescription that has recently gained support from close-binary observations. Different boosting ($K$) and disruption ($\eta$) parameters appear necessary for different systems, but their physical origins remain uncertain. We aim to identify the mechanisms that boost magnetic braking (MB) and cause its disruption at the fully convective boundary in cataclysmic variables (CVs). We modelled CV evolution with MESA and compared the results with observed CV properties. We computed the convective turnover time (${\tau }_c$) directly from the donor's structure rather than adopting empirical relations. We also included irradiation from the accreting white dwarf, which heats the donor's outer layers and can drive additional winds that enhance MB. The structure-based ${\tau }_c$ calculation reveals a pronounced spike as the donor approaches full convection, which drives the disruption parameter $\eta$ and initiates the period gap in CVs. The outcome of irradiation is sensitive to the accretion, irradiation, and wind efficiencies, all of which are poorly constrained from observations. Despite these uncertainties, plausible parameter choices allow irradiation-driven winds to provide the required boost $K$ during accreting phases. We refer to the combined prescription as the i$\tau$SBD MB model and find that it yields evolutionary tracks broadly consistent with the main CV properties. Our i$\tau$SBD MB framework offers a physically motivated interpretation of the empirical boost and disruption factors in SBD MB for CV evolution. We suggest that the convective turnover time spike at the fully convective boundary may drive MB disruption for fast-rotating stars in the saturated regime, while irradiation-driven winds may be the dominant mechanism boosting MB in accreting binaries and other strongly irradiated close systems.

15 pages, 10 figures, 1 table. Accepted for publication in A&A

References in corpus (36)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• The Donor Stars of Cataclysmic Variables
• The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs
• The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• New Observational Constraints on the Winds of M Dwarf Stars
• The origin and evolution of magnetic white dwarfs in close binary stars
• Stellar Winds on the Main-Sequence I: Wind Model
• Evolution of LMXBs under Different Magnetic Braking Prescriptions
• Relation of X-ray activity and rotation in M dwarfs and predicted time-evolution of the X-ray luminosity
• SW Sextantis stars: the dominant population of CVs with orbital periods between 3-4 hours
• On the proper use of the Schwarzschild and Ledoux criteria in stellar evolution computations
• The evolutionary status of Cataclysmic Variables: Eclipse modelling of 15 systems
• Evidence for reduced magnetic braking in polars from binary population models
• The Missing Magnetic Morphology Term in Stellar Rotation Evolution
• A catalogue of cataclysmic variables from 20 years of the Sloan Digital Sky Survey with new classifications, periods, trends and oddities
• Low Mass X-ray Binaries: The Effects of the Magnetic Braking Prescription
• Spectroscopic search for new SW Sextantis stars in the 3-4 hour orbital period range -- I
• Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF
• Evolution of intermediate-mass X-ray binaries driven by magnetic braking of Ap/Bp stars: I. ultracompact X-ray binaries
• Black widow evolution: magnetic braking by an ablated wind
• The cataclysmic variable orbital period gap: More evident than ever
• Cataclysmic variable evolution and the white dwarf mass problem: A Review
• Black widow formation by pulsar irradiation and sustained magnetic braking
• Magnetic braking with MESA evolutionary models in the single star and LMXB regimes
• A MeerKAT Survey of Nearby Novalike Cataclysmic Variables
• Rotation at the Fully Convective Boundary: Insights from Wide WD + MS Binary Systems
• A unified model for the evolution of cataclysmic variables
• Further evidence of saturated, boosted, and disrupted magnetic braking from evolutionary tracks of cataclysmic variables
• On the rapid orbital expansion in the compact low-mass X-ray binary 2A 1822$-$371
• Convective dynamos of black widow companions
• Measurement of stellar and substellar winds using white dwarf hosts
• A modest change in magnetic braking at the fully convective boundary explains cataclysmic variable evolution