Measurements of the Singly Ionized Oxygen Auroral Doublet Lines λλ7320, 7330 Using High‐Resolution Sky Spectra

The wavelengths of the individual [O II] 2s22p3 2Do(5/2) - 2s22p32Po(1/2,3/2) 7320\AA and [O II] 2s22p3 2Do(3/2) - 2s22p3 2Po(1/2,3/2) 7330\AAauroral doublet component lines have been measured directly in the nightglowfor the first time, from high resolution spectra obtained with the HIRESspectrograph on the Keck I telescope at the W.M. Keck Observatory.Specifically, we find 7320\AA and 7330\AA doublet splittings of1.077$\pm$0.003\AA and 1.080$\pm$0.003\AA respectively, with the formersignificantly larger than the often quoted and utilized value of 0.8\AA fromMoore (1949, Atomic Energy Levels, Vol 1), and in line with NIST (1.07\AA) aswell as more recent astrophysical observations of the lines in planetarynebulae including 1.07\AA from DeRobertis, Osterbrock, & McKee(1985,ApJ,293,459) and 1.09\AA from Barnett & McKeith (1988,MNRAS,234,241). Ourresults suggest, however, that adjustments of +0.124\AA and +0.131\AA should bemade to current NIST wavelengths for the blue and red components of the 7320\AAdoublet respectively, while the wavelengths of the 7330\AA doublet componentsare little changed from current NIST values. The observed intensity ratio of7320\AA/7330\AA from these measurements agrees with the theoretical valuecalculated under conditions of thermally populated 2Po levels.Comment: 16 pages, 4 tables, 1 figure, accepted by Ap