A comparison of theoretical Fe xii emission line strengths with EUV observations of a solar active region
Abstract
New theoretical electron-density-sensitive Fe XII emission line ratios R1 = I(3s23p34S3/2 - 3s3p44P5/2)/I(3s23p32P3/2 - 3s3p4D5/2 and R2 = I(3s23p32P3/2 - 3s3p42D5/2)/I(3s23p34S3/2 - 3s3p2P3/2) are derived using R-matrix electron impact excitation rate calculations. We have identified the FeXII and transitions in an active region spectrum obtained with the Harvard S-055 spectrometer on board Skylab at wavelengths of 364.0, 382.8, 1241.7, and 1349.4 Å, respectively. Electron densities determined from the observed values of R1 (log Ne ≃ 11.0) and R2(log Ne ≃ 11.4) are significantly larger than the typical active region measurements, but are similar to those derived from some active region spectra observed with the Skylab 2082A instrument, which provides observational support for the atomic data adopted in the line ratio calculations, and also for the identification of the Fe XII transitions in the S-055 spectrum. However the observed value of R3 = I(1349.4 Å)/I(1241.7 Å) is approximately a factor of two larger than one would expect from theory which, considering that the 1349.4 Å line lies at the edge of the S-055 wavelength coverage, may reflect errors in the instrument efficiency curve. Another possibility is that the 1349.4 Å transition is blended, probably with Si II 1350.1 Å.
- Publication:
-
Solar Physics
- Pub Date:
- October 1991
- DOI:
- 10.1007/BF00147507
- Bibcode:
- 1991SoPh..135..353K
- Keywords:
-
- Emission Spectra;
- Extreme Ultraviolet Radiation;
- Line Spectra;
- Solar Activity;
- Solar Spectra;
- Spectral Energy Distribution;
- Electron Transitions;
- Iron;
- Metallicity;
- Spectrometers;
- Solar Physics;
- Line Strength;
- Atomic Data;
- Efficiency Curve;
- Line Ratio;
- Impact Excitation