Planetary nebulae: the universal mass-metallicity relation for Local
  Group dwarf galaxies and the chemistry of NGC 205
  Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC
205 by using GMOS@Gemini spectra to derive their physical and chemical
parameters. The chemical patterns and evolutionary tracks for 14 of our PNe
suggest that there are no type I PNe among them. These PNe have an average
oxygen abundance of 12+log(O/H)=8.08$\pm$0.28, progenitor masses of
2-2.5M$_{\odot}$ and thus were born ~1.0-1.7Gyr ago. Our results are in good
agreement with previous PN studies in NGC 205. The present 12+log(O/H) is
combined with our previous works and with the literature to study the PN
metallicity trends of the Local Group (LG) dwarf galaxies, in an effort to
establish the PN luminosity- and mass-metallicity relations (LZR and MZR) for
the LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous
attempts to obtain such relations failed to provide correct conclusions because
were based on limited samples (Richer & McCall 1995; Gon\c{c}calves et al.
2007). As far as we are able to compare stellar with nebular metallicities, our
MZR is in very good agreement with the slope of the MZR recently obtained for
LG dwarf galaxies using spectroscopic stellar metallicities (Kirby et al.
2013). Actually, we found that both dIrr and dSph galaxies follow the same MZR,
at variance with the differences claimed in the past. Moreover our MZR is also
consistent with the global MZR of star-forming galaxies, which span a wider
stellar mass range ($\sim10^6$ - $\sim10^{11}$M$\odot$).
