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Fossil field decay due to nonlinear tides in massive binaries

Abstract : Surface magnetic fields have been detected in 5% to 10% of isolated massive stars, hosting outer radiative envelopes. They are often thought to have a fossil origin, i.e. inherited from the stellar formation phase. Yet, magnetic massive stars are scarcer in (close) short-period binaries, as reported by the BinaMIcS collaboration. Thus, different physical conditions in the molecular clouds giving birth to isolated stars and binaries are commonly invoked. Here, we suggest that the observed lower magnetic in binaries is due to nonlinear tides. Close binaries are likely prone to the tidal instability, a fluid instability growing upon the equilibrium tide via nonlinear effects. However, its outcome in radiative interiors is poorly understood. We investigate the tidal instability in rapidly rotating, stably stratified fluids permeated by fossil fields. First, we show that the tidal instability is generated by triadic resonances involving inertia-gravity waves in short-period massive binaries. Second, we build a mixing-length theory of the turbulent mixing generated by nonlinear tides. The predictions are confronted to proof-of-concept simulations. The typical time scale for the turbulent decay of a fossil field evolves as (beta0^2 Ws)^{-1}, with Ws the typical spin angular velocity of the fluid and beta0 the tidal amplitude. Hence, we predict that the tidal disruption of fossil fields would occur in less than a few million years for typical short-period massive binaries (with beta0 = 1e-3 - 1e-2). Therefore, the observed dearth of short-period magnetic binaries may be explained by the mixing generated by nonlinear tides.
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https://hal-insu.archives-ouvertes.fr/insu-02049328
Contributor : Jérémie Vidal Connect in order to contact the contributor
Submitted on : Tuesday, February 26, 2019 - 12:13:25 PM
Last modification on : Thursday, January 6, 2022 - 4:30:02 PM
Long-term archiving on: : Monday, May 27, 2019 - 2:31:23 PM

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2019_MNRAS_Vidal.pdf
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  • HAL Id : insu-02049328, version 1
  • ARXIV : 1902.10599

Citation

Jérémie Vidal, David Cébron, Asif Ud-Doula, Evelyne Alecian. Fossil field decay due to nonlinear tides in massive binaries. 2019. ⟨insu-02049328v1⟩

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