A new global instability of toroidal magnetic fields in stars is reported that grows on the Alfvén time, is less dissipation-sensitive than the Tayler instability, and may affect angular momentum transport.
The stability of toroidal fields in stars
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abstract
We present numerical models of hydromagnetic instabilities under the conditions prevailing in a stably stratified, non-convective stellar interior, and compare them with previous results of analytic work on instabilities in purely toroidal fields. We confirm that an $m=1$ mode (`kink') is the dominant instability in a toroidal field in which the field strength is proportional to distance from the axis, such as the field formed by the winding up of a weak field by differential rotation. We measure the growth rate of the instability as a function of field strength and rotation rate $\Omega$, and investigate the effects of a stabilising thermal stratification as well as magnetic and thermal diffusion on the stability. Where comparison is computationally feasible, the results agree with analytic predictions.
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Synthetic spectra show that observational biases cause dipole mode visibilities to be overestimated by up to 20 percent on the red-giant branch, while partial energy preservation under magnetic damping can produce both present and absent mixed-mode signatures.
A mean-field magnetic polytrope model shows radiation pressure can unbind an n=3 polytrope when the central overpressure exceeds roughly 0.15 times a mass-dependent factor under small radial perturbations.
citing papers explorer
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Beyond the Tayler instability: A new global instability of toroidal magnetic fields in stars
A new global instability of toroidal magnetic fields in stars is reported that grows on the Alfvén time, is less dissipation-sensitive than the Tayler instability, and may affect angular momentum transport.
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Oscillations of red giant stars with magnetic damping in the core. II. Mixed mode visibilities on the red-giant branch
Synthetic spectra show that observational biases cause dipole mode visibilities to be overestimated by up to 20 percent on the red-giant branch, while partial energy preservation under magnetic damping can produce both present and absent mixed-mode signatures.
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Non-linear Dynamical Stability of Magnetic Polytropes
A mean-field magnetic polytrope model shows radiation pressure can unbind an n=3 polytrope when the central overpressure exceeds roughly 0.15 times a mass-dependent factor under small radial perturbations.