THE FEATURES OF CHEMICAL ABUNDANCES IN GALACTIC PLANETARY-NEBULAE

The chemical composition of 217 Galactic planetary nebulae is investigated; 203 of them are subdivided into four classes according to the masses of nebulae and progenitor stars. The values of local abundances, Galactic abundance gradients and Galactic electron temperature gradients are found for each class of nebula. The correlations between the abundances of pairs of elements are also calculated for each class of nebula. The results are compared with theoretical predictions. In particular, it is concluded that CN cycling can play a role in progenitor stars for all classes of planetary nebula.