Atomic data for astrophysics: Ni XI^⋆

¹ DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 0WA, UK
e-mail: g.del-zanna@damtp.cam.ac.uk
² Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
³ Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK

Received: 17 March 2014
Accepted: 30 April 2014

Abstract

We present a new large-scale R-matrix scattering calculation for electron collisional excitation of Ni xi, carried out with the intermediate-coupling frame transformation method. The target includes all the main configurations up to n = 4, and is a significant improvement over earlier R-matrix (only three n = 3 configurations) and distorted-wave (DW) calculations. We find significant enhancements in the collision strengths of many of the strong transitions to the n = 3,4 levels. They are due to the resonances that arise within the present large-scale target. This results in significant increases in the predicted intensities of the UV and visible forbidden lines within the 3s²3p⁵3d configuration, the strong EUV lines that result from the decays of the 3s²3p⁵3d levels to the ground state, and the decays from the n = 4 levels, which are visible in the soft X-rays. We find good agreement between predicted and observed line intensities in the EUV. With the present atomic data, lines from Ni xi can reliably be used for plasma diagnostics. We also revise some level energies and suggest a few new possible identifications.