The Planetary Nebula Luminosity Function: Pieces of the Puzzle

Extragalactic surveys in the emission line of [O III] λ5007 have provided us with the absolute line strengths of large, homogeneous sets of planetary nebulae. These data have been used to address a host of problems, from the measurement of the extragalactic distance scale, to the study of stellar populations. I review our current understanding of the [O III] planetary nebula luminosity function (PNLF), and discuss some of the physical processes that effect its structure. I also describe the features of the Hα PNLF, a function that, upon first glance, looks similar to the [O III] PNLF, but which includes a very different set of objects. Finally, I discuss recent measurements of α, the number of PNe found in a stellar population, normalized to that population's bolometric luminosity. I show that, contrary to expectations, the values of α found in actively star-forming spirals are essentially the same as those measured in late-type elliptical and lenticular systems. I discuss how this result sheds light on the physics of the planetary nebula phenomenon.