Effect of log g on C iii 4647–50–51. Left panel: the red line is a model with log g = 3.5; the blue line is the same model with log g = 4.0. The effective temperature is 42 000 K. Right panel: departure coefficient of the upper and lower levels of C iii 4647–50–51 (upper panel) and of levels 2s^2 1S (n = 1), 2s2p ³P^o (n = 2,3,4), 2p2p ³D (n = 6,7,8) (lower panel) for log g = 3.5 (solid line) and log g = 4.0 (dashed line), plotted as a function of Rosseland opacity. The dotted line is the C iii 4650 formation region.