Astronomy & Astrophysics

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Issue		A&A Volume 430, Number 1, January IV 2005
Page(s)		331 - 341
Section		Atomic, molecular and nuclear data
DOI		10.1051/0004-6361:20041358

A&A 430, 331-341 (2005)
DOI: 10.1051/0004-6361:20041358

Atomic data from the IRON Project

LVI. Electron excitation of Be-like Fe XXIII for the n = 2, 3, 4 configurations

M. C. Chidichimo¹, G. Del Zanna¹, H. E. Mason¹, N. R. Badnell², J. A. Tully³ and K. A. Berrington⁴

¹ Department of Applied Mathematics and Theoretical Physics, The Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 OWA, Cambridge, UK
e-mail: G.Del-Zanna@damtp.cam.ac.uk
² Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK
³ Département Cassiopée, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
⁴ School of Science and Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK

(Received 26 May 2004 / Accepted 10 August 2004)

Abstract
Collision strengths for electron induced transitions in the beryllium-like ion Fe ⁺²² are calculated using the intermediate coupling frame transformation (ICFT) version of the R-matrix programs. Our target has 98 fine structure states ${\rm 1s^2}\,nl\,n'l'\,SLJ$ corresponding to n = 2 and n' = 2, 3, 4. The present calculation is for electron impact energies in the range 3.15 to 380 Ry. When T exceeds about ten million degrees one needs to take account of contributions to the thermally averaged collision strength $\sl\Upsilon$ coming from electrons with energies in excess of 380 Ry. We discuss a way of allowing for these contributions. Values of $\sl\Upsilon$ for all the transitions between the ground state and the excited states ${\rm 1s^2}\,2l\,n\,l\,n'l'\,S'L'J'$ , with n'=2,3,4 are tabulated as a function of ${\rm log}\,T$ . The temperature range $6.3 \le \log\, T \le 8.1$ is centred on ${\rm log}\,T = 7.1$ which is approximately where Fe ⁺²² has maximum abundance in ionization equilibrium. To the best of our knowledge these are the first R-matrix calculations for Fe ⁺²² for excitations to the n = 3,4 levels. Good agreement with previous distored-wave calculations is found. However, the resonance contributions have an important effect on the effective collision strengths and in turn on the level populations.

Key words: atomic data -- Sun: corona

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