S xi Emission Lines in Active Region Spectra Obtained with the Solar euv Rocket Telescope and Spectrograph (Serts) |
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| Authors: | Keenan FP Pinfield DJ Mathioudakis M Aggarwal KM Thomas RJ Brosius JW |
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| Institution: | (1) Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland;(2) Laboratory for Astronomy and Solar Physics, Code 682, NASA's/Goddard Space Flight Center, Greenbelt, MD, 20771, U.S.A.;(3) Raytheon ITSS, Lanham, MD, 20706, U.S.A. |
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| Abstract: | Theoretical electron density sensitive emission line ratios involving a total of eleven 2s
22p
2–2s2p
3 transitions in S xi between 187 and 292 Å are presented. A comparison of these with solar active region observations obtained during rocket flights by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals generally good agreement between theory and experiment. However, the 186.87 Å line is masked by fairly strong Fexii emission at the same wavelength, while 239.83 Å is blended with an unknown feature, and 285.58 Å is blended with possibly Niv 285.56 Å. In addition, the 191.23 Å line appears to be more seriously blended with an Fexiii feature than previously believed. The presence of several new Sxi lines is confirmed in the SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Å, in excellent agreement with laboratory measurements. In particular, the detection of the 2s
22p
2
3
P
1 –2s2p
3
3
P
0,1 transitions at 242.91 Å is the first time (to our knowledge) that this feature has been identified in the solar spectrum. The potential usefulness of the Sxi line ratios as electron density diagnostics for the solar transition region and corona is briefly discussed. |
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