Abstract
The controversy on the time variation of the radial abundance gradients can in principle be settled by estimating the gradients from planetary nebulae (PN) ejected by central stars (CSPN) with different ages. In this work, we consider four samples of CSPN whose lifetimes have been estimated using three different methods and estimate the oxygen abundance gradients for these objects. The results suggest some small differences between the younger and older CSPN. The younger objects have similar or slightly higher oxygen abundances compared with the older objects, and the gradients of both groups are similar within the uncertainties. Therefore, the O/H radial gradient has not changed appreciably during the lifetime of the objects considered, so that PN gradients are not expected to be very different from the gradients observed in younger objects, which seems to be supported by recent observational data.
