AAS 196th Meeting, June 2000
Session 43. Planetary Nebulae and Their Progenitors
Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

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[43.01] Bipolarity Without Binarity: AGB Winds, Dipole Magnetic Fields, and Disk Formation

S. Matt, B. Balick (Astronomy Department, University of Washington), R. Winglee, A. Goodson (Geophysics Department, University of Washington)

We present a simple, robust mechanism for producing an equatorially concentrated wind (excretion disk) from a non-rotating AGB or post-AGB star. This equatorial density enhancement (existing in a slow wind) presents an aspherical inertial barrier to subsequent fast, isotropic winds that may occur. Such a barrier may act as a nozzle for producing the axisymmetric (elliptical or bipolar) morphologies exhibited by many PNe without invoking merging binary systems or surface rotation near breakup.

In the presented model, the star initially has a dipole magnetic field that is inflated by the wind to become mostly radial but oppositely directed above and below the equator. The interaction between the wind plasma and magnetic field produce a steady-state outflow in which magnetic forces direct plasma toward the equator. We also present the results of MHD simulations that confirm the model.

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