Comparison of (effective) collision strengths (Υs, see the lower panel) Ωs from the ground state of S⁸⁺. BL03 refers to the distorted wave calculation by Bhatia & Landi (2003a), AS-DW refers to the present Breit-Pauli DW calculation using autostructure. Upper panel: scaled collision strength for a dipole transition 2s²2p⁴   3P₂  ←  2s²2p³3d   ³P₁ (1–80) with C = 2.0. The limit value is 4g_if_ij/E_ij at 1.0 for the dipole transition. Lower panel: the ratio of Υs between the results of the DW calculation by Bhatia & Landi (2003a) and the ICFT R-matrix calculation at log T_e (K) = 5.1, 6.1 (corresponding to peak abundance of S⁸⁺ in ionization equilibrium) and 7.1. The dashed lines correspond to agreement within 20%. The transition marked by dotted box is the dipole transition 1–80 shown in the upper panel. (Colour online.)