A Comparison of Theoretical Si VIII Emission Line Ratios with Observations from Serts |
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| Authors: | Keenan F.P. Katsiyannis A.C. Ramsbottom C.A. Bell K.L. Brosius J.W. Davila J.M. Thomas R.J. |
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| Affiliation: | (1) Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland;(2) Department of Applied Mathematics and Theoretical Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland;(3) Laboratory for Astronomy and Solar Physics, NASA's Goddard Space Flight Center, Code 682, Greenbelt, MD, 20771, U.S.A.;(4) Department of Physics, The Catholic University of America, Washington, DC, 20064, U.S.A. |
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| Abstract: | Recent R-matrix calculations of electron impact excitation rates in N-like Si VIII are used to derive theoretical emission line intensity ratios involving 2s22p3–2s2p4 transitions in the 216–320 Å wavelength range. A comparison of these with an extensive dataset of solar active region, quiet-Sun, sub-flare and off-limb observations, obtained during rocket flights of the Solar EUV Research Telescope and Spectrograph (SERTS), indicates that the ratio R1= I(216.94 Å)/I(319.84 Å) may provide a usable electron density diagnostic for coronal plasmas. The ratio involves two lines of comparable intensity, and varies by a factor of about 5 over the useful density range of 108–1011 cm?3. However R2= I(276.85 Å)/I(319.84 Å) and R3=I(277.05 Å)/I(319.84 Å) show very poor agreement between theory and observation, due to the severe blending of the 276.85 and 277.05 Å lines with Si VII and Mg VII transitions, respectively, making the ratios unsuitable as density diagnostics. The 314.35 Å feature of Si VIII also appears to be blended, with the other species contributing around 20% to the total line flux. |
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