Published in "The Analysis of Emission Lines",
eds. R. E. Williams and M. Livio, Space Telescope Science Institute
Symposium Series 8, 1995
For a postscript version of the article, click
here.
Abstract. Infrared emission lines are just coming into their own as diagnostic tools for the study of gaseous nebulae. Various infrared line ratios provide the means to determine physical parameters such as extinction, density, temperature, and ionic and elemental abundances. In certain regimes, infrared lines provide essentially the only opportunity for determining these parameters, or even for detecting the gas. Examples include regions of high extinction, low temperature, and predominantly neutral material. I review the general properties of infrared emission lines and their characteristics as nebular diagnostics, and cite a number of illustrative applications. The latter are drawn from a wide range of fields, including star formation and H II regions, planetary nebulae, nova and supernova remnants, shocked and photodissociated gas, and AGN and starburst galaxies.
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