Relative Coronal Abundances Derived From X-Ray Observations Ⅲ: The Effect of Cascades on the Relative Intensity of FeⅩⅦ Line Fluxes, and a Revised Iron Abundance

摘要

Permitted lines in the optically thin coronal X-ray spectrum can be analyzed to find the distribution of coronal material as a function of temperature without special assumptions concerning coronal conditions provided the relevant atomic rate constants are known. The helium-like and hydrogen-like resonance lines of N, O, Ne, Na, Mg, Al, Si, S, and Ar which dominate the quiet coronal spectrum below 25A have been observed from the U. S. Air Force satellites OV1-10 and OV1-17 and these observations have been used to construct coronal models and to determine the relative abundances of these elements. The theoretical atomic rate constants are relatively well known for these simple ions, and the coronal excitation condition, which assumes that excited states are populated by collision excitation from the ground state, should be well satisfied for resonance lines of these ions.