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Session 17 - The Galactic Interstellar Gas.
Display session, Monday, January 13
Metropolitan Ballroom,
We present a revision of the Emission Line Chart (Williams, 1995), which displayed selected emission lines of different ions excited under nebular conditions in a convenient format. We have calculated an extensive grid of photoionization models, covering a wide range of hydrogen densities (n_H) and stellar temperatures (T_*). The results of this grid are used to identify those line ratios which are insensitive to conditions in the gas and which are therefore good for deriving abundances. These ratios are highlighted on the revised chart, where we indicate in which region of the (n_H, T_*) plane they are most useful. We suggest that researchers give preference to utilizing these networks when deriving gas-phase abundances in emission-line objects.
