tokens: the differing resonance profiles converging on to differing threshold positions. The present calculation has shifted the thresholds to lie in their exact observed positions listed in Table 1 . In Fig. 6 we present the effective collision strengths for some higher lying transitions, the 3d 7 4 F 9/2 –3d 7 2 G 9/2 (1 → 8), 3d 7 2 P 1/2 –3d 7 2 H 9/2 (11 → 13) and 3d 7 2 G 7/2 –3d 7 2 H 9/2 (9 → 13). Excellent agreement is evident for all three transitions when a comparison is made with the data of Storey Sochi ( 2016 ) across all temperatures where a comparison is possible. The collision strengths and effective collision strengths for all 42 486 forbidden and allowed lines are available from the authors on request but we present in Table 4 the effective collision strengths for all transitions among the lowest 11 3d 7 fine-structure levels across nine temperatures of astrophysical importance. 1 Figure 6. The effective collision strengths, Υ 1 → 8 (top), Υ 11 → 13 (middle) and Υ 9 → 13 (bottom), presented as a function of temperature in K (bottom). Solid black lines with stars are the current data set and the dashed line with crosses represent the results from Storey Sochi ( 2016 ). Table 4. Effective collision strengths as defined by equation ( 5 ) are presented between an upper ( j ) and lower state ( i ), across a range of nine temperatures (K), 3800 T 25 100 K. We have denoted ( a ) ≡ ×10 a . 3.3 Line ratios Combining the electron-impact excitation rates with the decay rates ( A -values), it is possible to investigate important infrared and visible line ratios. For simplicity and purpose of this study, we neglect the recombination and ionization process from the neighbouring ion stages and focus on the populating mechanisms solely of Co iii . Assuming local thermal equilibrium and detailed balance, we can derive the collisional radiative modelling approach detailed in (Griffin et al. 1997 ). We can therefore investigate selected transitions that have been suggested as temperature or density diagnostics. We present in Table 5 a comparison of emissivities (ρ ij ) between our current results, and those from Storey Sochi ( 2016 ) for particular transitions at electron densities N e = 10 4 cm −3 and N e = 10 7 cm −3 . The emissivities are calculated relative to the H β line [see equation ( 1 ) in Storey Sochi ( 2016 )], where the effective recombination coefficients can be found in Hummer Storey ( 1987 ) and Storey Hummer ( 1995 ). The wavelengths are those from National Institute of Standards and Technology (NIST) and we use our current set of A -values. In general there is excellent agreement for all emissivities considered with the major outlier ρ 1 → 2 found to be around 30 per cent at N e = 10 4 cm −3 . This is evident from the strong Υ 1 → 2 from Fig. 5 (a) at T = 10 4 K. By replacing this one effective collision strength to Υ 1 → 2 ( T = 10 000) = 4.18, then the ρ 1 → 2 differences are within a much more agreeable 8 per cent. A similar
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