Electron Densities in the Solar Polar Coronal Holes from Density-Sensitive Line Ratios of SiⅧ and S Ⅹ

摘要

We derive electron densities as a function of height in the north and south polar coronal holes from a forbidden spectral line ratio of Si VIII. Si VIII is produced at about 8 * 10~5 K in ionization equilibrium. We also derive densities from a similar line ratio of S X (1.3 * 10~6 K). The spectra were obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft. In addition to the primary mechanism of electron impact excitation, the derivation of theoretical level populations for Si VIII and S X includes both proton and resonance capture excitation.