SIMBAD references

We have created a master list of Zanstra temperatures for 373 galactic planetary nebulae based upon a compilation of 1575 values taken from the published literature. These are used to evaluate mean trends in temperature for differing nebular morphologies. Among the most prominent results of this analysis is the tendency for η=T_Z(Heii)/T_Z(Hei) to increase with nebular radius, a trend which is taken to arise from the evolution of shell optical depths. We find that as many as 87 per cent of nebulae may be optically thin to H ionizing radiation where radii exceed ∼0.16 pc. We also note that the distributions of values η and T_Z(Heii) are quite different for circular, elliptical and bipolar nebulae. A comparison of observed temperatures with theoretical H-burning tracks suggests that elliptical and circular sources arise from progenitors with mean mass <M_PG>≅ 1 M_☉ (although the elliptical progenitors are probably more massive). Higher-temperature elliptical sources are likely to derive from progenitors with mass ≅2 M_☉, however, implying that these nebulae (at least) are associated with a broad swathe of progenitor masses. Such a conclusion is also supported by trends in mean galactic latitude. It is found that higher-temperature elliptical sources have much lower mean latitudes <b > than those with smaller T_Z(Heii), a trend which is explicable where there is an increase in <M_PG> with increasing T_Z(Heii). This latitude-temperature variation also applies for most other sources. Bipolar nebulae appear to have mean progenitor masses ≅2.5 M_☉ , whilst jets, Brets and other highly collimated outflows are associated with progenitors at the other end of the mass range (<M_PG>∼ 1 M_☉). Indeed it is possible, given their large mean latitudes and low peak temperatures, that the latter nebulae are associated with the lowest-mass progenitors of all.

The present results appear fully consistent with earlier analyses based upon nebular scale heights, shell abundances and the relative proportions of differing morphologies, and offer further evidence for a link between progenitor mass and morphology.