Rotation and Stability of the Toroidal Magnetic Field in Stellar Radiation Zones

Bonanno, A.; Урпин, В. А.

doi:10.1088/0004-637x/766/1/52

Cited by 11 publications

(5 citation statements)

References 24 publications

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“…The magnetism in the radiative interior arises both from diffusive imprinting of field from the overlying convection zone (similar to the fast MHD confinement scenario), and also from local inductive amplification by strong horizontal motions. This dynamo action occurs even below the convective overshoot layer, a phenomenon also suggested by prior mean-field calculations (e.g., Dikpati & Gilman 2001;Spruit 2002;Bonanno & Urpin 2013) and explored in global dynamo simulations (e.g., Racine et al 2011;Lawson et al 2015). In our simulation, the horizontal motions in the radiative interior are due to equatorially confined (equatorial) Rossby waves (Gizon et al 2020) and possibly shear, magnetic, and buoyancy instabilities as well.…”

Section: Introductionsupporting

confidence: 79%

Confinement of the Solar Tachocline by Dynamo Action in the Radiative Interior

Matilsky

Hindman

Featherstone

et al. 2022

ApJL

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A major outstanding problem in solar physics is the confinement of the solar tachocline, the thin shear layer that separates nearly solid-body rotation in the radiative interior from strong differential rotation in the convection zone. Here, we present the first 3D, global solar simulation that displays a magnetically confined tachocline. The nonaxisymmetric magnetism is initially built in the convection zone and then diffusively imprints downward, similar to the proposed fast magnetic confinement scenario by the Sun’s cyclic dynamo field. Additionally, the field is locally amplified throughout the radiative interior by vigorous horizontal motions that seem to arise from a combination of equatorial Rossby waves and shear, magnetic, and buoyancy instabilities. Our work thus supports prior studies proposing dynamo action in the radiative interior, and suggests that horizontal motions could play a key role in driving this deep dynamo.

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Section: Introductionsupporting

confidence: 79%

Confinement of the Solar Tachocline by Dynamo Action in the Radiative Interior

Matilsky

Hindman

Featherstone

et al. 2022

ApJL

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“…The first attempt to address the spherical symmetry can be found in Goossens et al (1981) using a WKB approximation in radius. The role of rotation has been discussed in Kitchatinov (2008) and subsequently in Kitchatinov & Rüdiger (2008), where it was shown that the instability is essentially three-dimensional, as also confirmed by Bonanno & Urpin (2013b). The specific role of gravity has been discussed in detail in Bonanno & Urpin (2012).…”

Section: Stability Considerationsmentioning

confidence: 89%

“…MHD instabilities in stable stratified stellar plasmas might also play a central role in the transport of angular momentum in radiative zones, explaining the slow rotation of the core of the red giants (Beck et al 2012;Triana et al 2017), the suppression of the dipolar mixed modes in the core of the red giants (Fuller et al 2015), and as source of an α-effect in the solar tacochline (Arlt et al 2007;Guerrero et al 2019). From linear analysis we have learnt that rotation plays a stabilizing role (Pitts & Tayler 1985;Bonanno & Urpin 2013a) while thermal diffusivity tends to oppose to the stabilizing role of gravity, and the resulting growth rates are of the order of the evolutionary time scales according to Bonanno & Urpin (2012). The use of direct numerical simulations to determine stable field configurations has to be properly motivated, as the choice of the basic state can play an essential role in the growth rate and the non-linear evolution of the instabilities.…”

mentioning

confidence: 99%

Global simulations of Tayler instability in stellar interiors: the stabilizing effect of gravity

Gómez

Sordo

Bonanno

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Unveiling the evolution of toroidal field instability, known as Tayler instability, is essential to understand the strength and topology of the magnetic fields observed in early-type stars, in the core of the red giants, or in any stellar radiative zone. We want to study the non-linear evolution of the instability of a toroidal field stored in a stably stratified layer, in spherical symmetry and in the absence of rotation. In particular, we intend to quantify the suppression of the instability as a function of the Brunt-Väisäla (ω BV ) and the Alfvén (ω A ) frequencies. We use the MHD equations as implemented in the anelastic approximation in the EULAG-MHD code and perform a large series of numerical simulations of the instability exploring the parameter space for the ω BV and ω A . We show that beyond a critical value gravity strongly suppress the instability, in agreement with the linear analysis. The intensity of the initial field also plays an important role: weaker fields show much slower growth rates. Moreover, in the case of very low gravity, the fastest growing modes have a large characteristic radial scale, at variance with the case of strong gravity, where the instability is characterized by horizontal displacements. Our results illustrate that the anelastic approximation can efficiently describe the evolution of toroidal field instability in stellar interiors. The suppression of the instability as a consequence of increasing values of ω BV might play a role to explain the magnetic desert in Ap/Bp stars, since weak fields are only marginally unstable in the case of strong gravity.

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“…The extensive literature on Tayler instability is mainly focused on the stability criteria and growth rates of unstable disturbances as the most significant characteristics of the instability (see, e.g. Goossens et al 1981;Spruit 1999;Braithwaite 2006;Kitchatinov & Rüdiger 2008;Bonanno & Urpin 2013a;Guerrero et al 2019, and references therein). Apart from the growth rates, eigenvalues of the linear stability problem include the oscillation frequency.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal drift of Tayler instability eigenmodes as a possible explanation for super-slowly rotating Ap stars

Kitchatinov

Potravnov

Nepomnyashchikh

2020

A&A

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Context. Rotation periods inferred from the magnetic variability of some Ap stars are incredibly long, exceeding ten years in some cases. An explanation for such slow rotation is lacking. Aims. This paper attempts to provide an explanation of the super-slow rotation of the magnetic and thermal patterns of Ap stars in terms of the longitudinal drift of the unstable disturbances of the kink-type (Tayler) instability of their internal magnetic field. Methods. The rates of drift and growth were computed for eigenmodes of Tayler instability using stellar parameters estimated from a structure model of an A star. The computations refer to the toroidal background magnetic field of varied strength. Results. The non-axisymmetric unstable disturbances drift in a counter-rotational direction in the co-rotating reference frame. The drift rate increases with the strength of the background field. For a field strength exceeding the (equipartition) value of equal Alfven and rotational velocities, the drift rate approaches the proper rotation rate of a star. The eigenmodes in an inertial frame show very slow rotation in this case. Patterns of magnetic and thermal disturbances of the slowly rotating eigenmodes are also computed. Conclusions. The counter-rotational drift of Tayler instability eigenmodes is a possible explanation for the observed phenomenon of super-slowly rotating Ap stars.

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Rotation and Stability of the Toroidal Magnetic Field in Stellar Radiation Zones

Cited by 11 publications

References 24 publications

Confinement of the Solar Tachocline by Dynamo Action in the Radiative Interior

Confinement of the Solar Tachocline by Dynamo Action in the Radiative Interior

Global simulations of Tayler instability in stellar interiors: the stabilizing effect of gravity

Longitudinal drift of Tayler instability eigenmodes as a possible explanation for super-slowly rotating Ap stars

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