Laboratory Measurements of the Fe xvii 2 p –3 s and 2 p –3 d Transitions and Comparison with Solar and Astrophysical Observations

Abstract

The L-shell emission spectrum of Fe XVII is measured in high-temperature laboratory plasmas, and the inferred intensities of the 3s → 2p transitions relative to those of the dominant 3d → 2p transition are compared to solar observations, as well as to observations of Capella, Procyon, Castor C, II Pegassi, and NGC 4636 with the Chandra and XMM-Newton X-ray observatories. The results from laboratory and astrophysical plasmas are in very good agreement, indicating that the collisional line formation processes found in low-density, high-temperature laboratory plasmas are a good description of those found in astrophysical plasmas. The laboratory observations disagree, however, to varying degrees with spectral modeling calculations. A review of existing laboratory measurements suggests that the intensity of the dominant 3d → 2p transition is overestimated by spectral modeling predications. By calibrating spectral models with laboratory data, especially by decreasing the strength of the dominant 3d → 2p transition, spectral models can be brought into agreement with the majority of solar and astrophysical observations. Without doing so, opacity effects may be grossly overestimated.