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.
