This work presents estimates of the effects that magnetic fields might have on non-convective mixing phenomena in red giants of low mass. We discuss recent doubts on the effectiveness of purely rotationally-induced mixing and an alternative idea is illustrated, according to which kink modes of buoyant, toroidal magnetic flux tubes might guarantee matter circulation. This occurs not through downward motions from the envelope (as assumed so far), but through different buoyancy efficiencies of tubes born at different depths in the radiative zone, carrying upward material exposed to partial H burning. We adopt a simple formalism to estimate the strength of the magnetic fields necessary to guarantee cool bottom processes and the formation of the neutron source 13C , which drives slow neutron captures in AGB stars. Our rough estimates do not allow final conclusions, but we find that the required magnetic field strengths are in the range foreseen for the stages and zones of interest. This tells us that the mechanisms here indicated are worth the (considerable) effort of a full MHD treatment. For the moment, magnetic fields are to be seen as a promising possibility for solving the mystery of red giant mixing.

Can extended mixing in red giants be attributed to magnetic mechanisms?

M.C. NUCCI;
2004

Abstract

This work presents estimates of the effects that magnetic fields might have on non-convective mixing phenomena in red giants of low mass. We discuss recent doubts on the effectiveness of purely rotationally-induced mixing and an alternative idea is illustrated, according to which kink modes of buoyant, toroidal magnetic flux tubes might guarantee matter circulation. This occurs not through downward motions from the envelope (as assumed so far), but through different buoyancy efficiencies of tubes born at different depths in the radiative zone, carrying upward material exposed to partial H burning. We adopt a simple formalism to estimate the strength of the magnetic fields necessary to guarantee cool bottom processes and the formation of the neutron source 13C , which drives slow neutron captures in AGB stars. Our rough estimates do not allow final conclusions, but we find that the required magnetic field strengths are in the range foreseen for the stages and zones of interest. This tells us that the mechanisms here indicated are worth the (considerable) effort of a full MHD treatment. For the moment, magnetic fields are to be seen as a promising possibility for solving the mystery of red giant mixing.
2004
M.M. BUSSO; M.C. NUCCI; A. CHIEFFI; O. STRANIERO
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/916175
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