HEATING THE HALOES OF PLANETARY-NEBULAE

Three planetary nebulae have extended haloes which have measured electron temperatures considerably in excess of those measured for the corresponding cores. We suggest that this is caused by the shocking of a mildly supersonic flow exiting from the core against clumps of material in the halo regions. This flow is produced as a fast stellar wind mass-loads as it percolates through core regions containing clumps of previously ejected material. This model predicts temperature fluctuations of 5-10 x 10(3) K in the halo regions and that the regions of enhanced temperature will be dynamically inert. Recent measurements of the linewidths in the halo of NGC 6543 are in agreement with this model. This type of flow may also be responsible for the accelerated haloes which have been observed in several planetary nebulae.