Several evolutionary channels for bright planetary nebulae
  The populations of bright planetary nebulae in the discs of spirals appear to
differ in their spectral properties from those in ellipticals and the bulges of
spirals. The bright planetary nebulae from the bulge of the Milky Way are
entirely compatible with those observed in the discs of spiral galaxies. The
similarity might be explained if the bulge of the Milky Way evolved secularly
from the disc, in which case the bulge should be regarded as a pseudo-bulge.
