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Stothers, R.B., 2004: Magnetic influence on the stability of luminous stellar envelopes. Astrophys. J., 607, 999-1002, doi:10.1086/383535.
Turbulence in the convective outer envelope of a luminous post-main-sequence star probably shreds any magnetic field that is buoyed up from the radiative region below and probably also generates small local magnetic fields. These magnetic structures would consist of well-tangled field lines, but could at most attain a steady state strength based on a near equipartition of their mean energy with the turbulent kinetic energy. Even assuming the maximum possible strength, the magnetic fields turn out to be too weak to affect significantly the dynamical stability of the envelope. This is a consequence as much of the low value of the field strength as of the fact that the field responds hydrodynamically to radial perturbations in the same manner as a gas with an adiabatic exponent of 4/3. Furthermore, fields this small are found to barely affect the radiative stability of the envelope. If the strongest magnetic components could safely reach the atmosphere, however, they might exert a noticeable effect there, or if the whole radiative interior were permeated with a strong magnetic field, very rapid mass loss at the surface might keep the outer layers strongly magnetic at all times before turbulence could break up the field lines. Otherwise, the bulk of the outer envelopes in stars such as yellow hypergiants, luminous blue variables, and hydrogen-poor Wolf-Rayet stars are not expected to be strongly magnetic.
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