Comparison between the spectrum from CALSPEC and from our model for Vega. Top panel: spectra of Vega from CALSPEC and from our model (orange and blue lines, respectively; left scale) and energy transmission curves of the filters used to compute the colour indices (right scale). The Strömgren filters are shown as dashed lines, while the HST filters as solid lines, the colours having the same meaning as in Figs. 7 and 9, respectively, except that the u filter is replaced here by u′. Bottom panel: difference between the flux of our Vega model and that of CALSPEC (black solid line).