The correlation between planetary nebula morphology and radio brightness temperatures

We have used model central star evolutionary tracks to evaluate the expected variation of 5 GHz brightness temperatures TB in planetary nebulae. Using these results, and previously derived central star mass functions, we find that there should be a correlation between TB and the mean central star mass MCS, and also between TB and nebular morphology. An analysis of the available observational results suggests that such a correlation between TBand nebular morphology does indeed exist. Bipolar nebulae appear to be concentrated towards high brightness temperatures, whilst circular sources tend to possess lower brightness temperature shells. Elliptical sources are present (and common) at all values of TB. There are differences however between the observed and deduced morphological variations, and these enable us to place constraints upon the progenitor masses of the nebulae. In particular, it is clear that higher mass progenitors are likely to give rise to both bipolar and elliptical outflows; a result which is consistent with analyses of nebular abundances, Zanstra temperatures, and line excitations.