Turbulent dynamo in asymptotic giant branch stars

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 alphaomega dynamos, the rotation has only a small role in amplifying the toroidal component of the magnetic field; instead of an alphaomega dynamo we propose an alpha(2)omega. The magnetic field may reach a value of B similar or equal to 10(-4)B(e) similar or equal to 0.01 G, where B-e is the equipartition (between die 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.