Chemical abundances of photoionized nebulae in the Local Group
  Photoionized nebulae comprise basically HII regions and planetary nebulae,
and their abundances give important clues on the nucleosynthesis and chemical
evolution of their host galaxies. There is presently a large amount of data on
these objects, especially for the elements He and N, which are strongly
affected by the evolution of intermediate mass stars, as well as O, Ne, S, and
Ar, which are essentially synthesized in stars with larger masses. The
abundances of these elements in several systems in the Local Group are
discussed on the basis of distance-independent correlations.
