Influence of Resonances on Spectral Formation of X-Ray Lines in Fe XVII

Abstract

New theoretical results from large-scale relativistic close coupling calculations reveal the precise effect of resonances in collisional excitation of x-ray lines of Ne-like Fe XVII. Employing the Breit-Pauli R-matrix method and a 89-level eigenfunction expansion including up to n = 4 levels shows significant resonance enhancement of the collision strengths of forbidden and intercombination transitions. The present results differ from all previous calculations, heretofore without detailed resonance structures, and should help resolve longstanding discrepancies. In particular, the present line ratios of three benchmark diagnostic lines 3C, 3D, and 3E at 15.014, 15.265, and 15.456 A respectively, are in excellent agreement with two independent measurements on Electron-Beam-Ion-Traps [Laming et al, Astrophys. J, 545, L161 (2000) and Brown et al, Astrophys. J, 502, 1015 (1998)]. The strong energy dependence due to resonances in these and other cross sections is demonstrated for the first time. It is of general importance and strongly manifests itself in x-ray plasma diagnostics.