MASS-LOADED FLOWS .7. TRANSONIC-FLOWS FROM THE CORES OF PLANETARY-NEBULAE

We present simple analytical and more detailed numerical models of the flow resulting from the mass loading of a fast stellar wind in the co re region of a planetary nebula. It is found that, for mass-loading ra tes above a critical value, the flow leaving the core will always be t ransonic. We suggest that this mass-loading model provides a simple ex planation for the observed high electron temperatures in the haloes of some planetary nebulae. The model has been applied to the core-halo p lanetary nebula NGC 6543. It is found that the mass-loading rate requi red to ensure a transonic flow leaving the core does not conflict with estimates of the available progenitor mass.