Possible Identification of Permitted Fe XIV Lines in the Extreme Ultraviolet Solar Spectrum.

The physical conditions and composition of the corona lead one to expect that permitted Fe XIV lines should appear with considerable strength in the extreme ultraviolet solar spectrum. Earlier attempts at identification have been quite uncertain and incomplete. Satellite observations, such as the OSO-1 data used here, have the advantage over rocket observations in permitting the study of line in tensity variations during solar activity. We have tentatively identified several lines in the extreme ultraviolet as due to Fe XIV on the basis of almost identical enhancements relative to background and other lines with increased plage activity. The lines we attribute to Fe XIV lie at wavelengths within 2 A of wavelengths predicted from the energy levels computed by Garstang (Ann. d'Astrophys. 25,109, 1962). Exceptions are the 3p 2P0-3d2D transitions, which we suggest may actually lie 10 A toward shorter wavelengths. In every case, however, the separation of the term intervals agree within a few hundred wave numbers with the predicted values. The absence of the resonance lines, expected at XX 345, 366, 368, may be due to their rather low oscillator strengths, as computed by Garstang, and to the decreased sensitivity of the OSO-1 spectrometer at these wavelengths. The relative intensities of the observed lines agree only very approximately with Garstang's calculations. The lines observed are: Predicted Observed Transition J-J wavelength wavelength 3p2P~3p22S 1/2-1/2 272.9 274 3/2-1/2 287.7 289 3p 2P~3p2 2~ 1/2-1/2 256.0 Blended (He ii) 1/2-3/2 250.5 252 3/2-1/2 269.0 270.5 3/2-3/2 262.9 264 3p2P~3d2D 1/2-3/2 214.1 204 3/2-3/2 223.1 211 3/2-5/2 222.0 211