Planetary Nebulae as Probes of Stellar Populations

Aside from their utility as distance indicators, planetary nebulae are also a unique tool with which to probe the stellar populations of a galaxy. When normalized to bolometric luminosity, non-star-forming stellar populations should have an evolutionary flux (defined as the number of stars per unit time evolving through a given phase) of ~ 2 x 10^{-11} stars/yr/L(sun), independent of age, metallicity, or initial mass function. For typical PN lifetimes of 25,000 years, this number implies that every galaxy should have alpha(2.5) = 50 x 10^{-9} PN/L(sun) within the top 2.5 mag of the planetary nebula luminosity function. The fact that some galaxies display far fewer PN than predicted (by a factor of ~5) implies that PN number counts can be used to discriminate between different stellar populations.

For information on how the production of bright PN correlations with galaxy properties, and why [O III]-bright planetaries exist at all in elliptical galaxies, check out

Web page by Robin Ciardullo ( rbc@astro.psu.edu )
Department of Astronomy and Astrophysics
Penn State University