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A Comparison of Theoretical Si VIII Emission Line Ratios with Observations from Serts

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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 2s 22p 3–2s2p 4 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 R 1= 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 R 2= I(276.85 Å)/I(319.84 Å) and R 3=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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Authors and Affiliations

  1. Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland

    F.P. Keenan & A.C. Katsiyannis

  2. Department of Applied Mathematics and Theoretical Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland

    C.A. Ramsbottom & K.L. Bell

  3. Laboratory for Astronomy and Solar Physics, NASA's Goddard Space Flight Center, Code 682, Greenbelt, MD, 20771, U.S.A.

    J.W. Brosius, J.M. Davila & R.J. Thomas

  4. Department of Physics, The Catholic University of America, Washington, DC, 20064, U.S.A.

    J.W. Brosius

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  1. F.P. Keenan
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  2. A.C. Katsiyannis
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  3. C.A. Ramsbottom
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  4. K.L. Bell
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Keenan, F., Katsiyannis, A., Ramsbottom, C. et al. A Comparison of Theoretical Si VIII Emission Line Ratios with Observations from Serts. Solar Physics 219, 251–263 (2004). https://doi.org/10.1023/B:SOLA.0000023001.61242.e1

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  • DOI: https://doi.org/10.1023/B:SOLA.0000023001.61242.e1

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