THE PLANETARY-NEBULA LUMINOSITY FUNCTION

This talk gives a brief introduction to the subject of the planetary nebula luminosity function (PNLF) and its use for extragalactic distance determinations. After describing the essential features of the early work by Jacoby, Ciardullo, Ford and collaborators, a list of objections is given. The relevance of these objections is analyzed using a simple procedure for the numerical simulation of the PNLF. The bright end of the PNLF turns out to be affected by sample size, by population characteristics and by the extent to which stellar ionizing photons are able to escape unabsorbed by the nebula. Although the PNLF method may be less accurate than previously thought, the distances determined by Jacoby, Ciardullo et al. are not significantly affected; in particular, the PNLF method still gives a distance of 15 Mpc to the Virgo cluster.