Yu.V.Lunyova, A.F.Kholtygin
Chemical evolution of the system of galactic planetrary nebulae, Astrophysics, 45, 451-463 (2002)

Chemical evolution of the system of galactic planetary nebulae beginning from the early age of the Galaxy is investigated. We calculate radial and vertical abundance gradients of C, N, O, Ne, Ar, Cl and S depending of different ages of the central star of the nebula. It have been founded statistically significant dependence of abundance gradients with the age of central star.