Electron densities above a polar coronal hole based on improved Si IX density diagnostics |
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Authors: | Doyle JG Keenan FP Ryans RSI Aggarwal KM Fludra A |
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Institution: | (1) Armagh Observatory, Armagh, BT61 9DG, N. Ireland;(2) Department of Pure and Applied Physics, Queens University Belfast, Belfast, BT7 1NN, N. Ireland;(3) Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK |
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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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