Comparison between the molecular light curves of CN (see text) and HCN (from Drahus et al. 2011). The HCN signal is represented by the line area measured in the beam of 8.8-arcsec FWHM. The light curves are calculated with respect to the mean levels, and phased according to the 18.32 h period. The filled symbols are used for CN and the open symbols for HCN, while the symbol shape indicates the three-cycle component. The error bars for CN are of the order of the symbol size and have been omitted.