The adiabatic stability of stars containing magnetic fields - VI. The influence of rotation

Pitts, E.; Tayler, R. J.

doi:10.1093/mnras/216.2.139

Cited by 168 publications

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“…Elaborating on results of earlier investigations of instabilities of toroidal magnetic fields in stars conducted by Tayler and others (e.g., Tayler 1973;Markey & Tayler 1973, 1974Acheson 1978;Pitts & Tayler 1985), Spruit (1999) has proposed a new magnetohydrodynamic mode of angular momentum transport in radiative zones of differentially rotating stars. Fluid elements experience large-scale horizontal displacements caused by an unstable configuration of the toroidal magnetic field (one consisting of stacks of rings concentric with the rotation axis).…”

Section: Introductionmentioning

confidence: 80%

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A Revised Prescription for the Tayler‐Spruit Dynamo: Magnetic Angular Momentum Transport in Stars

Denissenkov

Pinsonneault

2007

ApJ

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Angular momentum transport by internal magnetic fields is an important ingredient for stellar interior models. In this paper we critically examine the basic heuristic assumptions in the model of the Tayler-Spruit dynamo, which describes how a pinch-type instability of a toroidal magnetic field in differentially rotating stellar radiative zones may result in large-scale fluid motion. We agree with prior published work both on the existence of the instability and its nearly horizontal geometry for perturbations. However, the approximations in the original Acheson dispersion relation are valid only for small length scales, and we disagree that the dispersion relation can be extrapolated to horizontal length scales of order the radius of the star. We contend that dynamical effects, in particular, angular momentum conservation, limit the maximum horizontal length scale. We therefore present transport coefficients for chemical mixing and angular momentum redistribution by magnetic torques that are significantly different from previous published values. The new magnetic viscosity is reduced by 2-3 orders of magnitude compared to the old one, and we find that magnetic angular momentum transport by this mechanism is very sensitive to gradients in the mean molecular weight. The revised coefficients are more compatible with empirical constraints on the timescale of core-envelope coupling in young stars than the previous ones. However, solar models including only this mechanism possess a rapidly rotating core, in contradiction with helioseismic data. Previous studies had found strong core-envelope coupling, both for solar models and for the cores of massive evolved stars. We conclude that the Tayler-Spruit mechanism may be important for envelope angular momentum transport but that some other process must be responsible for efficient spin-down of stellar cores.

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Section: Introductionmentioning

confidence: 80%

“…In this case, the Coriolis force reduces the instability's growth rate considerably by a factor of ! A / T1 (Pitts & Tayler 1985).…”

Section: Revised Heuristic Assumptions and Transport Coefficientsmentioning

confidence: 99%

A Revised Prescription for the Tayler‐Spruit Dynamo: Magnetic Angular Momentum Transport in Stars

Denissenkov

Pinsonneault

2007

ApJ

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“…The limiting case of a shellular rotational profile is rigid rotation. From the calculations by Maeder & Meynet (2005), it follows that magnetic fields created by the Pitts & Tayler instability (Pitts & Tayler 1985;Spruit 1999Spruit , 2002 can lock the stellar layers to each other and force the star to evolve as a rigid rotator. However, Zahn et al (2007) concluded that the dynamo action can be less efficient as previously expected (Spruit 1999(Spruit , 2002 and that the magnetic fields created contribute little or less to the transport of the angular momentum.…”

Section: Rotational Law In the Stellar Envelopementioning

confidence: 99%

Differential rotation in rapidly rotating early-type stars

Zorec

Frémat

Souza

et al. 2010

A&A

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Context. Since the external regions of the envelopes of rapidly rotating early-type stars are unstable to convection, a coupling may exist between the convection and the internal rotation. Aims. We explore what can be learned from spectroscopic and interferometric observations about the properties of the rotation law in the external layers of these objects. Methods. Using simple relations between the entropy and specific rotational quantities, some of which are found to be efficient at accounting for the solar differential rotation in the convective region, we derived analytical solutions that represent possible differential rotations in the envelope of early-type stars. A surface latitudinal differential rotation may not only be an external imprint of the inner rotation, but induces changes in the stellar geometry, the gravitational darkening, the aspect of spectral line profiles, and the emitted spectral energy distribution. Results. By studying the equation of the surface of stars with non-conservative rotation laws, we conclude that objects undergo geometrical deformations that are a function of the latitudinal differential rotation able to be scrutinized both spectroscopically and by interferometry. The combination of Fourier analysis of spectral lines with model atmospheres provides independent estimates of the surface latitudinal differential rotation and the inclination angle. Models of stars at different evolutionary stages rotating with internal conservative rotation laws were calculated to show that the Roche approximation can be safely used to account for the gravitational potential. The surface temperature gradient in rapid rotators induce an acceleration to the surface angular velocity. Although a nonzero differential rotation parameter may indicate that the rotation is neither rigid nor shellular underneath the stellar surface, still further information, perhaps non-radial pulsations, is needed to determine its characteristics as a function of depth.

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“…In rotating stars under the condition ω A Ω, the growth time scale of the magnetic instability is (Pitts & Tayler 1986;Spruit 1999) …”

Section: Magnetic Effectsmentioning

confidence: 99%

Angular momentum transport and element mixing in the stellar interior

Yang

2006

A&A

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Aims. The purpose of this work was to obtain diffusion coefficient for the magnetic angular momentum transport and material transport in a rotating solar model. Methods. We assumed that the transport of both angular momentum and chemical elements caused by magnetic fields could be treated as a diffusion process. Results. The diffusion coefficient depends on the stellar radius, angular velocity, and the configuration of magnetic fields. By using of this coefficient, it is found that our model becomes more consistent with the helioseismic results of total angular momentum, angular momentum density, and the rotation rate in a radiative region than the one without magnetic fields. Not only can the magnetic fields redistribute angular momentum efficiently, but they can also strengthen the coupling between the radiative and convective zones. As a result, the sharp gradient of the rotation rate is reduced at the bottom of the convective zone. The thickness of the layer of sharp radial change in the rotation rate is about 0.036 R in our model. Furthermore, the difference of the sound-speed square between the seismic Sun and the model is improved by mixing the material that is associated with angular momentum transport.

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The adiabatic stability of stars containing magnetic fields - VI. The influence of rotation

Cited by 168 publications

References 0 publications

A Revised Prescription for the Tayler‐Spruit Dynamo: Magnetic Angular Momentum Transport in Stars

A Revised Prescription for the Tayler‐Spruit Dynamo: Magnetic Angular Momentum Transport in Stars

Differential rotation in rapidly rotating early-type stars

Angular momentum transport and element mixing in the stellar interior

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