Left panels: CCFs of the integrated Balmer lines in blue, the integrated He I λ5876 line in orange and the integrated He II λ4686 line in red, with respect to the continuum light curve at 5100 Å. The time lag, τ_cent, is denoted by a dashed line; the shaded area corresponds to a ±1σ interval from the Monte-Carlo simulations. Right panels: Cross-correlation centroid distributions after 20 000 runs employing FR and RSS of the integrated Balmer lines in blue, the integrated He I λ5876 line in orange and the integrated He II λ4686 line in red, with respect to the continuum at 5100 Å.