Best fitting models (thick black line) for the N v doublet and N iv line in the spectrum of V1 (upper panels) and V5 (lower panels). The observed spectra (grey) are smoothed over a six pixels width (one resolution element) in this figure and the following ones. Right panels: as a comparison, model spectra with a lower (red) and higher (blue) temperature are shown. Left panels: with model spectra having a lower (red) and higher (blue) nitrogen abundance.