Detection of [N [CSC]ii[/CSC]] λ5755 Emission from Low-Density Ionized Interstellar Gas

Abstract

The extremely faint, temperature-sensitive ``auroral'' emission line [N II] lambda5755 has been detected from the low-density ionized gas along the sight line toward l=130.0d, b=-7.5d using the Wisconsin Halpha Mapper. The intensity of this emission line, relative to the red nebular line [N II] lambda6584, is found to be twice that observed in bright, classical H II regions surrounding O stars. This implies that the electron temperature of the ionized gas along this sight line is about 2000 K higher than the H II regions and that the enhanced [N II] lambda6584/Halpha and [S II] lambda6716/Halpha intensity ratios in this low-density gas are due at least in part to an elevated temperature.