Overplot of the four selected profiles of N v (top), Si iv (middle), and C iv (bottom) of σ Lup. The two doublet rest wavelengths are indicated by vertical dashed lines. Top scale: wavelength. Bottom scale: velocity with respect to the stellar rest frame. In each panel the lower part displays the significance of the variability, expressed as the square root of the ratio of the measured to the expected variances. The changes are very similar to what is observed in known magnetic B stars (see Fig. 1), but not in other B stars.