Abstract
The maximum luminosity, the chemical abundance ratios, and the internal kinematics of the nebular shells of bright extragalactic planetary nebulae are all rather insensitive to the underlying stellar populations in any given galaxy. These similarities argue that the brightest planetary nebulae arise from similar progenitor stars, but this is not necessarily expected theoretically given the metallicities and star formation histories of their host galaxies. However, there are consistent, if small, differences in luminosity and kinematics that do depend upon the host galaxy's stellar populations, notably its metallicity. These differences imply that we necessarily observe the brightest planetary nebulae in different galaxies in different evolutionary stages, with the brightest planetary nebulae from elliptical galaxies and the bulges of spirals being observed in an earlier stage. Therefore, there must exist multiple evolutionary pathways to produce the intrinsically brightest planetary nebulae.
