Galactic radial abundance gradients: cepheids and photoionized nebulae

Radial abundance gradients are observed in the Galaxy and other galaxies as well, and include several chemical elements in different stellar systems. Possibly the most accurate gradients in the Galaxy are those determined from chepheid variable stars. These objects have very accurate abundances for many elements and are generally considered as standard candles, so that their galactocentric distances are very well determined. These stars are relatively young, with ages between the main types of photoionized nebulae, namely the younger HII regions and the older planetary nebulae. In this paper we consider the O/H and Fe/H gradients based on a large sample of galactic cepheids, and compare the results with recent determinations from photoionized nebulae.