Extragalactic Planetary Nebulae: tracers of the chemical evolution of   nearby galaxies
  The study of the chemical composition of Planetary Nebulae in external galaxies is of paramount importance in the fields of stellar evolution and of the chemical enrichment history of galaxies. In the last years a number of spectroscopic studies with 6-8m-class telescopes have been devoted to this subject improving our knowledge of, among other, the time-evolution of the radial metallicity gradient in disk galaxies, the chemical evolution of dwarf galaxies, and the stellar evolution at low metallicity. 
Laura Magrini, Letizia Stanghellini, Denise R. Goncalves
astro-ph.CO astro-ph.GA