Extragalactic Planetary Nebulae

Abstract

It is a great pleasure for me to be able to start off this “Joint Discussion” on Extragalactic Planetary Nebulae. Many astronomers appear somewhat ambivalent in their attitudes towards planetary nebulae. A few of us regard planetaries as the spectacular “last hurrah” before stars slide off into oblivion as white dwarfs. Others think of them as soaring butterflies that evolved from stellar caterpillars. Finally a few less romantic astronomers simply ask “what can planetary nebulae do for us?” Perhaps surprisingly the answer is that they can do a great deal for the progress of various branches of astronomy. At this meeting George Jacoby will, for example, show us how planetary nebulae can be used to measure extragalactic distances. Mike Dopita, Ziaohui Hui and Ken Freeman will tell us that planetaries are powerful probes of the kinematics of galaxies. Furthermore Henry Ferguson will show how planetary nebulae can be used to probe the effects of metallicity on stellar evolution in elliptical galaxies.