GRAVITY DISTANCES OF PLANETARY-NEBULAE

Recent work on the PN classification scheme initially proposed by Peim bert has shown that ''type I'' and ''non-type I'' objects have markedl y different properties. Type I PN have He and N enrichments, lower hei ghts relative to the galactic plane, and lower peculiar velocities, wh ile non-type I nebulae have normal abundances and increasing heights a nd peculiar velocities. This implies some mass and age differences of the different types, which can be used in order to determine distances to disk PN. In this work, the behaviour of PN of different types on t he log g x log T-eff plane is explored, in view of the fact that centr al stars of different masses have different paths on this diagram. As a result, distances can be derived for some galactic PN, which can be compared with previous determinations. The possibility is discussed of establishing a statistical distance scale based on the population seg regation of PN of different Peimbert types.