Cross-correlation functions of total brightness radial series at PA = 263° for some of the successive observation instants, labeled as t_n. The lag value corresponds to the annulus position gap considered. The top-left panel shows the autocorrelation function of the radial series obtained at the instant t₁. In the other panels, the cross-correlation functions between the radial series at instant t_n and the radial series at instant t₁ are reported. In each panel, the two instants at which the cross-correlated radial series have been collected are indicated in the top left. The red point in each panel highlights the maximum value of the cross-correlation function.