Emergent intensity from the surface of ϕ Dra at various rotational phases at wavelengths of 1400 Å (left panel), 2500 Å (middle panel), and in the U-band of the ten-colour system (right panel). The intensities are displayed as −2.5log (I/I₀), where I₀ is a reference intensity chosen in such a way that the resulting logarithm, averaged over the entire stellar surface, is equal to zero.