The purpose of this section is to provide a very brief introduction to abundance determinations from HII regions. My target audience consists of stellar astronomers that might like to connect their abundance studies to those of nebular astronomers, but might be somehow put-off by the trappings of a culture that is somewhat foreign.
Let me insert here a few philosophical statements about nebular abundances and the community of researchers that work on them. It is my impression that the confidence in abundances derived from nebular spectra is vastly different between people that work in the field and those that do not, in the sense that people that work in the field hold nebular abundance measurements to be quite reliable while outsiders consider them suspect. I think that there is a simple misinterpretation which is responsible. For those of us in the field, there is nothing more interesting than a small bit that we don't understand. I put forward as an example temperature fluctuations in nebulae. Temperatures in nebulae cannot be perfectly uniform, there must be fluctuations at some level. Due to the asymmetric temperature dependence of collisional excitation rates, if the fluctuations are large enough, then this will give rise to abundance under-estimates (Peimbert 1967). The problem is to determine the size and importance of this effect. Workers within the field are fascinated with this problem and have dedicated a good deal of work to it. For example, in a wonderful review by Peimbert (1995) several pages are spent describing this problem, while very little is said about the security and utility of the standard abundance measurements. Researchers outside of the field see all of this activity and may believe that all nebular abundance determinations are suspect since the problem of temperature fluctuations is not completely solved.
It is my feeling that, in many cases, this is throwing away the baby with the bath water. Nebular abundances are quite frequently measured with an accuracy more than necessary to provide meaningful constraints on a wide variety of astrophysical problems. I am campaigning to encourage the nebular community to remember to spread this message.