Photometric variability of the continuum features defined in Fig. 2. We note that N and S indicate the northern and southern lobe, respectively, and PD is the ring-like feature. The numbers increase from south-east to north-west. We note that S is further subdivided into S1 and S2, and S1 is in turn subdivided into S1a and S1b. The symbol size is ~0.2 mag in the vertical direction, which is comparable with the photometric errors. A sinusoid of period ~12 yr is overlaid on the N1 light curve. The same, but with a phase shift of π, is also drawn in the bottom box.