Astron. Astrophys. Suppl. Ser. 131, 145-152

Forbidden transitions in Li-like ions: Compact effective collision strengths for ${\rm 2s} - n{\rm s},n{\rm d}$ where $n = 3,\, 4,\, 5$

A. Burgess¹ - M.C. Chidichimo² - J.A. Tully³

1 - Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW, UK
e-mail: ab10@damtp.cam.ac.uk
2 - Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
e-mail: mchidich@math.uwaterloo.ca
3 - Département G.D. Cassini, Observatoire de la Côte d'Azur, BP. 4229, 06304 Nice Cedex 4, France
e-mail: tully@obs-nice.fr

Received September 25, 1995; accepted January 2, 1998

Abstract:

Using an extension of the method for compacting atomic data set out by Burgess & Tully (1992), we make concise fits to a selection of the set of collision strengths ${\sl \Omega}$ given by Zhang et al. (1990) for Li-like ions from O⁺⁵ to U⁺⁸⁹. We carry out thermal averaging and fit the resulting effective collision strengths ${\sl \Upsilon}$. A compact $5\times5$ or $4\times4$ table of cardinal values for each transition allows one to reproduce the T and Z dependent ${\sl \Upsilon}$ to better than 1 per cent. The present study is for the forbidden transitions $\rm 2s \to 3s,4s,5s$ and $\rm 2s \to 3d,4d,5d$.

Key words: Li-like ions -- electron excitation -- compact atomic data