Observed N V λλ4603, 4619 and N III λλ4634, 4640 (blue solid line) compared to best-fitting model composition. In the upper panel, the nitrogen abundance of the primary is varied, while the secondary’s nitrogen abundance is kept at six times solar. In the lower panel, the secondary’s nitrogen abundance is varied, while the primary’s nitrogen abundance is kept at eight times solar. The red dashed lines indicate the final model.