2002MNRAS.329..204S -
Mon. Not. R. Astron. Soc., 329, 204-208 (2002/January-1)
Turbulent dynamo in asymptotic giant branch stars.
SOKER N. and ZOABI E.
Abstract (from CDS):
Using recent results on the operation of turbulent dynamos, we show that a turbulent dynamo may amplify a large-scale magnetic field in the envelopes of asymptotic giant branch (AGB) stars. We propose that a slow rotation of the AGB envelope can fix the symmetry axis, leading to the formation of an axisymmetric magnetic field structure. Unlike solar-type αω dynamos, the rotation has only a small role in amplifying the toroidal component of the magnetic field; instead of an αω dynamo we propose an α2ω. The magnetic field may reach a value of B≃10^-4B_e≃0.01 G, where Be is the equipartition (between the turbulent and magnetic energy densities) magnetic field. The large-scale magnetic field is strong enough for the formation of magnetic cool spots on the AGB stellar surface. The spots may regulate dust formation, and hence the mass-loss rate, leading to axisymmetric mass loss and the formation of elliptical planetary nebulae (PNe). Despite its role in forming cool spots, the large-scale magnetic field is too weak to play a dynamic role and directly influence the wind from the AGB star, as required by some models. We discuss other possible problems in models where the magnetic field plays a dynamic role in shaping the AGB winds, and argue that they cannot explain the formation of non-spherical PNe.
Abstract Copyright:
The Royal Astronomical Society
Journal keyword(s):
stars: AGB and post-AGB - circumstellar matter - stars: magnetic fields - stars: mass-loss - planetary nebulae: general
Simbad objects:
2
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