Radial velocities of the components D (red) and S (blue) of the CS Ca  II K narrow absorption features for all the observations. The sinusoidal curves plotted as pale red and blue have the only purpose toshow, in a qualitative way, that the behaviour of the RVs shows a periodic pattern during the ~ 32-yr interval covered by the observations. The exact treatment of the data is explained in Sect. 6.2. The labels indicate the instruments with which the observations were obtained (see Sect. 4).