Top: p₀ as a function of the limb-darkening parameter u_λ. The red box indicates the uncertainty on p₀ for the δ Scuti AI Vel. The blue box indicates the typical values of u_λ and p₀ for Cepheids. The dots corresponds to the relation provided by Nardetto et al. (2006). Bottom: p₀ as a function of the inclination of the fast rotating star β Cas for three different wavelengths (λ = 6000 Å (□), λ = 6500 Å ( △ ), and λ = 7000 Å ( × )). The red box indicates the uncertainty on p₀ for β  Cas. The case of an uniform elonged disc is over-plotted ( + ), and we find that p₀ = 1.5 for i = 0°, as expected for a circular uniform disc.