Planetary Nebulae and Chemical Evolution of the Galaxy

Abstract

The chemical evolution of galaxies is controlled by star formation, stellar mass loss, gas flows, and the compositions of matter involved in these processes. Planetary nebulae (PN) thus affect chemical evolution directly in representing mass ejection at the end of the nuclear burning lives of many stars, and in enriching the interstellar medium in elements that are overabundant in the nebulae. Supernovae often eclipse PN in discussions of these effects, so it is noteworthy that planetary precursor stars not only provide much of the present stellar mass loss in the solar neighborhood, but also show as clear evidence as supernova remnants for the ejection of elements newly synthesized in the stars themselves. Furthermore, PN are tracers of the past star formation history in a galaxy, since their rate of occurrence depends on the birthrate of progenitor stars during the whole lifetime of the system.