Measurements of the Singly Ionized Oxygen Auroral Doublet Lines $\lambda\lambda$7320,7330\AA Using High Resolution Sky Spectra

Abstract

The wavelengths of the individual [O II] 2s22p3 2Do(5/2) - 2s22p3 2Po(1/2,3/2) 7320\AA and [O II] 2s22p3 2Do(3/2) - 2s22p3 2Po(1/2,3/2) 7330\AA auroral doublet component lines have been measured directly in the nightglow for the first time, from high resolution spectra obtained with the HIRES spectrograph on the Keck I telescope at the W.M. Keck Observatory. Specifically, we find 7320\AA and 7330\AA doublet splittings of 1.077$\pm$0.003\AA and 1.080$\pm$0.003\AA respectively, with the former significantly larger than the often quoted and utilized value of 0.8\AA from Moore (1949, Atomic Energy Levels, Vol 1), and in line with NIST (1.07\AA) as well as more recent astrophysical observations of the lines in planetary nebulae including 1.07\AA from DeRobertis, Osterbrock, & McKee (1985,ApJ,293,459) and 1.09\AA from Barnett & McKeith (1988,MNRAS,234,241). Our results suggest, however, that adjustments of +0.124\AA and +0.131\AA should be made to current NIST wavelengths for the blue and red components of the 7320\AA doublet respectively, while the wavelengths of the 7330\AA doublet components are little changed from current NIST values. The observed intensity ratio of 7320\AA/7330\AA from these measurements agrees with the theoretical value calculated under conditions of thermally populated 2Po levels.