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Oscillations of magnetic stars: II. Axisymmetric toroidal and non-axisymmetric shear Alfven modes in a spherical shell

D. Reese·F. Rincon·M. Rieutord
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Abstract

We carry out numerical and mathematical investigations of shear Alfven waves inside of a spherical shell filled with an incompressible conducting fluid, and bathed in a strong dipolar magnetic field. We focus on axisymmetric toroidal and non-axisymmetric modes, in continuation of a previous work by Rincon & Rieutord (2003, A&A, 398, 663). Analytical expressions are obtained for toroidal eigenmodes and their corresponding frequencies at low diffusivities. These oscillations behave like magnetic shear layers, in which the magnetic poles play a key role, and hence become singular when diffusivities vanish. It is also demonstrated that non-axisymmetric modes are split into two categories, namely poloidal or toroidal types, following similar asymptotic behaviours as their axisymmetric counterparts when the diffusivities become arbitrarily small.

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D. Reese, F. Rincon, M. Rieutord. 2004-12-01. Oscillations of magnetic stars: II. Axisymmetric toroidal and non-axisymmetric shear Alfven modes in a spherical shell. https://doi.org/10.1051/0004-6361%3A20040539

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