Photometry of star A, as in the right panel of Fig. 3. Legend: grey dots are historical data from 1986 to 2005. Grey hexagons: first dimming. Grey triangles: between the two dimming events. Grey pentagons: second dimming. Green star and green triangle: photometry of stars A and B, respectively, from A15. Brown triangle: star B from WG01. Magenta star: star A from our X-shooter spectrum. All points are in the Johnson system. The coloured filled circles show photometric points closer than two days to the spectrographic observations with UVES and X-shooter. The colour code is reported in Table 1.