Electron Density and Nitrogen Abundance from FIR Lines

In order to study the physical properties of nebulae and determine their elemental abundances, it is important to observe lines from many different ionic species. Such studies have been enhanced in recent years with the measurement of lines in the far-infrared (FIR). The [N III]57μm line provides a way to assess the N ++ abundance – which is not readily done from any other spectral region. Recent detection of the [N II]122 and 205μm lines provides a new way to assess both the electron density in the N + region and the total N abundance in an object. When there are few observations to warrant a detailed modeling approach, it may be necessary to use another approach which has been referred to as a semi-empirical method (hereafter SEM) ( e.g. Aller 1984). We delineate a SEM scheme for doing this and apply it to observations for the H II region G333.6–0.2.