Theoretical Siivline ratios compared to extreme ultraviolet solar observations

✍ Scribed by F. P. Keenan; J. G. Doyle

• Publisher: Springer
• Year: 1988
• Tongue: English
• Weight: 326 KB
• Volume: 115
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00148725

✦ Synopsis

New theoretical electron temperature sensitive emission line ratios in SilV involving the 3d2D -3p2p and 4s2S -3pZP multiplets at ~ 1125 and 816 h, respectively, are derived using recent R-matrix electron excitation rate calculations. A comparison of these with observational data for a solar active region at the limb obtained with the Harvard S-055 spectrometer on board Skylab reveals that there is good agreement between theory and observation for ratios that include the 2D3/2, 5/2 -2P3/2 transition at 1128.3 A. This is in contrast to the findings of Keenan, Dufton, and Kingston (1986) and provides support for the atomic data adopted in the calculations. However, the 21)3/2 -~P1/2 line at 1122.5 A appears to be severely blended, as suggested previously by Burton and Ridgeley (1970) and Feldman and Doschek (1977), as it leads to electron temperature estimates that differ significantly from that expected in ionisation equilibrium. The fact that the I(1122.5 A)/I(1128.3 A) intensity ratios determined from several flare spectra are closer to theory than that for the active region indicates that the blending is probably due to species with relatively low ionization potentials, as noted by Flower and Nussbaumer (1975). Electron temperatures deduced for a sunspot are much lower than that predicted from ionisation balance calculations, in agreement with earlier results, and imply that a cooling flow may be present.