Effect of N v λλ1238-1242 on the derived nitrogen abundance. Panels a and b compare the nitrogen abundance of the presumed single stars, derived from the optical-only runs, to that derived from the optical + UV fits in case of excluding N V λλ1238-1242 (panel a) and in case of including N V λλ1238-1242 (panel b). In the fits where N V λλ1238- 1242 is included, the nitrogen abundance is systematically higher than the values found from the optical-only runs. In panel c) we show, as an example, the N V λλ1238-1242 doublet of Sk –67°167, with the best fit model of the optical + UV run including N V λλ1238-1242 (blue solid line), a model where we altered the nitrogen abundance to the optical- only best fit value (orange dashed line), and a model where, in addition, the X-ray volume filling fraction was increased (red dotted line). The models with a high nitrogen abundance and low X-ray volume filling fraction, and a lower nitrogen abundance and higher X-ray volume filling fraction are very similar and both match the observed spectrum.