Abstract
Using new close-coupling excitation rates for the C-like ion Si ix, density-diagnostic ratios based on Si ix lines have been re-evaluated and applied to a sequence of CDS observations taken above a polar coronal hole. The derived electron densities are in excellent agreement with previous values of Neestimated from the N-like ion Si viii for another coronal hole. The confirmed trend is for a fall-off of one order of magnitude within the first 0.3 R⊙above the limb. These densities are well fitted with an analytic formula for the density profile out to at least 8 R⊙, by which stage the electron density has fallen to ∼4×103 cm−3, from 1.5×108 cm−3at 1.0 R⊙.
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Doyle, J., Keenan, F., Ryans, R. et al. Electron densities above a polar coronal hole based on improved Si IX density diagnostics. Solar Physics 188, 73–80 (1999). https://doi.org/10.1023/A:1005190912529
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DOI: https://doi.org/10.1023/A:1005190912529