Intensity correlations of the 4278-A N2+(0-1) first negative band and 5875-A emissions in auroras

Simultaneous photometric observations of emission intensities in the 4278-Å N2+(0-1) first negative band and in the 5875-Å spectral region were made at Poker Flat, Alaska, for a short period during March 1972. Intensities measured in the 5875-Å region, where the (2p³P-3d³D) transition of He is expected to appear as a result of alpha particle precipitation, exhibited a nearly constant ratio of 1/20 of the 4278-Å N2+ band emission intensity over a wide intensity range. The observed emission in the 5875-Å region is attributable mainly to emission from strong lines of the O2+(2-2) first negative band and the N2(9-5) first positive band. No evidence was found for emission from He. The existence of time-varying auroral emission of presumably molecular origin, in addition to the background emission contributed by OH bands near the 5876-Å He transitions, places even more severe constraints upon photometric detection and identification of the auroral He emission than were previously anticipated. It is concluded that auroral He emission intensities in the 5875-Å spectral region must greatly exceed 1/20 of the 4278-Å intensity in order to be measured adequately by photometric techniques.