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Fig. 7


Equivalent width and peak velocity of the He ii emission during the 19982014 events in direct view to the star and in the reflected spectra at FOS4 (squares: HST STIS, diamonds: VLT UVES, triangles: Gemini GMOS, asterisks: CTIO 1.5 m CHIRON). Cycles are shifted by multiples of 2023 days. The values at FOS4 are corrected for the additional light travel time (tFOS4 = t + 18 d) and for the moving-mirror effect (Δv = 100 km s-1), see Sect. 2. The vertical lines indicate the timing of the approximate He ii peak emission. For the second He ii flare, we indicate two timings, labeled “2.” for the second peak in 2009 and 2014 and labeled “2.” for the assumed timing of the second peak in previous events based on the X-ray light curve and constraints from our spectra.

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