A CATALOG HEII-4686 LINE-INTENSITIES IN GALACTIC PLANETARY-NEBULAE

We have compiled the intensities of the HeII 4686 lines measured in Ga lactic planetary nebulae. We present a few observational diagrams rela ted to this parameter, and discuss them with the help of theoretical d iagrams obtained from simple model planetary nebulae surrounding evolv ing central stars of various masses. We determine the hydrogen and hel ium Zanstra temperature for all the objects with accurate enough data. We argue that, for Galactic planetary nebulae as a whole, the main ca use for the Zanstra discrepancy is leakage of stellar ionizing photons from the nebulae.