Detection of [N II] lambda 5755 emission from low-density ionized interstellar gas

The extremely faint, temperature-sensitive "auroral" emission line [N II] l ambda 5755 has been detected from the low-density ionized gas along the sig ht line toward = 130.0 degrees, b = -7.5 degrees using the Wisconsin H alph a Mapper. The intensity of this emission line, relative to the red nebular line [N II] lambda 6584, is found to be twice that observed in bright, clas sical H II regions surrounding O stars. This implies that the electron temp erature of the ionized gas along this sight line is about 2000 K higher tha n the H II regions and that the enhanced [N II] lambda 6584/H alpha and [S II] lambda 6716/H alpha intensity ratios in this low-density gas are due at least in part to an elevated temperature.