W. J. Maciel -
Abstract #67
ABUNDANCE GRADIENTS FROM PLANETARY NEBULAE IN THE GALACTIC DISK
W. J. Maciel
Planetary Nebulae, IAU Symposium 180, ed. H. J. Habing, H. J. G. L. M. Lamers, Kluwer, Dordrecht, 397-404 (1997) Radial abundance gradients in the disks of spiral galaxies are made evident from observations of ionized nebulae (HII regions, planetary nebulae, and SNRs) and stars. They have been observed for several chemical elements, and their presence is an established fact, despite some inconsistencies in the results. In this paper, a review is given of the main observation evidences for radial abundance gradients in the Galaxy and in spiral galaxies as well. Planetary nebulae are emphasized, particularly regarding the gradients of O/H, S/H, Ne/H, and Ar/H. The main problems of the interpretation of the gradients are discussed, such as inhomogeneities of the samples, distance scale, contamination by the PN central stars, and space and time variations of the gradients.
