Left panel: absorption lines develop a second blue component with a cycle of about 850 d. Three cycles have been observed so far; see also Fig. 6. Gray dotted lines indicate Fe i lines. Right panel: V-band magnitude (black squares) at the time of the spectra to the left (average of ± 1 d around the time of the spectrum). The radial velocity of the blue wing with respect to the red wing of the line is shown (green squares); measurements were performed at the midpoint (between maximum and minimum depths of the lines).