Laboratory Identification of Temperature Diagnostic Si VII and S IX Lines Present in the Solar Coronal Spectra Measured by SUMER/SOHO

Abstract

The solar coronal spectrum between 500 and 1610 Å and at a height of 21,000 km above the west equatorial limb has recently been recorded by the SUMER instrument on SOHO. Using laboratory spectra obtained with the beam-foil technique, we report the identification of 32 lines observed in this spectrum as 2s²2p³3s-2s²2p³3p and 2s²2p³3p-2s²2p³3d transitions in Si VII and S IX. Theoretical gA-values and branching ratios for the observed lines, obtained from semiempirical configuration interaction calculations, are also presented. Intensity ratios between the 2s²2p^{4 3}P₁-2s²2p^{4 1}S₀ forbidden transition and transition from the newly identified high-excitation lines that appear in the same wavelength range are temperature sensitive. Calculations of the intensity ratios between the forbidden line and the high-excitation lines for three temperatures are presented. A comparison between the calculations and some of the SUMER observations is provided.