Periodicity of the residual light curve modulation. Top: phase dispersion minimization evaluated in the frequency range between 0.4 and 0.9 c/d. Bottom: Lomb-Scargle periodogram (amplitude in ppm versus frequency in cd⁻¹) for the residuals of KELT-1, showing only the frequency range where most of the power lies. Overplotted in blue is the fit of a Gaussian function over the power to estimate an error for ν_min. The vertical orange line indicates the measured projected rotation velocity of the star as determined by Siverd et al. (2012). For comparison, the frequency of the orbital motion of KELT-1b is 0.821 c/d.