Diagnostic Utility of the Relative Intensity of 3C to 3D in F[CLC]e[/CLC] [CSC]xvii[/CSC]

Abstract

The relative intensity R of the resonance and intercombination line in neon-like Fe XVII, located at 15.01 and 15.26 Å, respectively, has been measured at the Lawrence Livermore National Laboratory electron beam ion trap EBIT-II as a function of the relative abundance of sodium-like Fe XVI. Our measurements identify several Fe XVI lines and one Fe XV line in this region. We show that an Fe XVI inner shell satellite line coincides with the intercombination line and can significantly reduce the apparent R. We measure R = 1.90 ± 0.11 when the relative abundance of Fe XVI to Fe XVII is ~1. This explains the anomalously low ratios observed in the solar and stellar coronae. The fact that the apparent relative intensity of the resonance and intercombination line in Fe XVII is sensitive to the strength of an Fe XVI inner shell satellite, and therefore, the relative abundance of Fe XVI to Fe XVII, makes the line ratio a diagnostic of temperature.