Optimal coherence is searched for a temporal remapping of the data set presented in Fig. 13 around the pre-estimated rotational period. Optimality is based on the spread of the cloud in three dimensions (binned data in time modulo Prot, intensity, velocity). It can be seen that Prot = 0.678 d corresponds to the best matching period (blue line). To assess significance we used the same data set with a randomly permutated time data set (green dots).