Turbulent dynamo in asymptotic giant branch stars

Noam Soker*, Essam Zoabi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


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 ≃ 10-4Be ≃ 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.

Original languageEnglish
Pages (from-to)204-208
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1 Jan 2002
Externally publishedYes


  • Circumstellar matter
  • Planetary nebulae: general
  • Stars: AGB and post-AGB
  • Stars: magnetic fields
  • Stars: mass-loss

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