Author(s): , , , ,
Institution(s): 1. INAOE, 2. Instituto de Astronomía, UNAM, 3. Observatoire de Meudon
The oxygen abundance in planetary nebulae (PNe) is traditionally used as a proxy of the interstellar medium metallicity at the time the PN progenitor stars were born. However, the nucleosynthesis processes occurring in AGB stars can alter the initial abundance of oxygen in the outer layers of the star that are ejected as a PN. Since these changes are more efficient at low metallicities, it is generally assumed that the abundance of oxygen is not significantly altered in PNe located at environments where the metallicity is close to solar or higher, such as the solar neighborhood or the Galactic bulge.
We present here our recent analysis of a group of 20 Galactic PNe belonging to the bulge, the halo and the solar neighborhood. These objects have high quality optical and infrared spectra that allow us to calculate reliable chemical abundances and to classify them as objects with either carbon-rich or oxygen-rich dust. We find that all but one of the PNe with carbon-rich dust show evidence of oxygen self enrichment even at near-solar metallicities. Our study indicates that oxygen is not always a reliable indicator of the original metallicity; other elements, such as chlorine and argon, should be used instead.