SIMBAD references

Planetary nebulae are known to possess a broad range of abundances, and these (with other characteristics) have been used to define five classes of outflow. Peimbert Type I sources, for instance, possess high N and He abundances, filamentary structures, and low mean scaleheights above the Galactic plane, whilst those of Type III have much lower abundances, high peculiar velocities, and belong to the Galactic thick disc. Apart from some rather ill-defined indications, however, very little is known concerning their mean physical, spatial, structural, kinematic and thermal characteristics.

We have performed a comprehensive study of all of these properties, and find evidence for strong variations between the various Peimbert classes. Certain of these differences are consistent with Type I sources having the highest progenitor masses, although it seems that these nebulae also possess the lowest rms densities and 5-GHz brightness temperatures. The latter results are in conflict with a range of recent modelling.