  In view of their nature, planetary nebulae have very short lifetimes, and the
chemical abundances derived so far have a natural bias favoring younger
objects. In this work, we report physical parameters and abundances for a
sample of old PNe located in the galactic bulge, based on low dispersion
spectroscopy secured at the SOAR telescope using the Goodman Spectrograph. The
new data allow us to extend our database including older, weaker objects that
are at the faint end of the planetary nebula luminosity function (PNLF). The
results show that the abundances of our sample are lower than those from our
previous work. Additionally, the average abundances of the galactic bulge do
not follow the observed trend of the radial abundance gradient in the disk.
These results are in agreement with a chemical evolution model for the Galaxy
recently developed by our group.
