tokens: Strassmeier 2012 ) observed in total 11 transits in five observing seasons using the filters Johnson B and Sloan r ′. The first seven transits were observed with both filters alternating. These r ′ band light curves were already published by Seeliger et al. ( 2014 ). The four light curves from 2014 to 2016 were taken only in Johnson B . WiFSIP holds a back-illuminated 4k × 4k 15 μm pixel CCD and offers a field of view (FoV) of 22 arcmin ×22 arcmin. To minimize the read-out time, a windowing of the CCD was used reducing the FoV to about 15 arcmin × 15 arcmin. A small defocus was applied to spread the point spread function to an artificial full width at half-maximum (FWHM) of about 3 arcsec. One transit was observed with the NOT as a Fast Track program using ALFOSC in imaging mode. ALFOSC contains a 2k × 2k E2V CCD providing an FoV of 6.4 arcmin × 6.4 arcmin. One transit was observed with BUSCA, the four-channel imager at the Calar Alto Observatory 2.2 m telescope (Reif et al. 1999 ). The instrument performs simultaneous photometry in four different bandpasses with an FoV of 11 arcmin × 11 arcmin. For the bandpass of shortest wavelength, we used a white glass filter and the beam splitter defined the limit of λ 430 nm. For the other bandpasses from blue to red, we used a Thuan–Gunn g , Thuan–Gunn r , and Bessel I filter. Unfortunately, the observation of a pre-ingress baseline was lost due to weather, and the observing conditions remained to be non-photometric. We discarded the light curve of shortest wavelength because it exhibited significantly larger correlated noise than the other three light curves. One transit was observed with the IAC80 telescope, owned and operated by the Instituto de Astrofísica de Canarias (IAC), using its wide field imager CAMELOT. It is equipped with a CCD-E2V detector of 2k × 2k, with a pixel scale of about 0.3 arcsec pixel −1 providing an FoV of about 10.5 arcmin × 10.5 arcmin. Two transits were observed with the 70 cm telescope of the AIP, located in the city of Potsdam at the Babelsberg Observatory. The telescope is equipped with a cryogenic cooled 1k × 1k TEK-CCD providing an FoV of 8 arcmin × 8 arcmin. The first transit was observed in Johnson B and Johnson V quasi-simultaneously with alternating filters, the second one in Johnson V only. We applied a 3 × 3 pixel binning to reduce the detector read-out time. Data of an additional transit were taken with the triple beam, frame-transfer CCD camera ULTRACAM (Dhillon et al. 2007 ) mounted at the WHT. The instrument optics allow for the simultaneous photometry in three different bandpasses. We chose the filters Sloan u ′, Sloan g ′, and a filter centred on the sodium doublet at 591.2 nm with a width (FWHM) of 31.2 nm. To avoid saturation of the brightest stars, the exposure time was extremely short with 0.3 s. However, the overheads are negligible owing to the frame-transfer technique. The detectors were read out in windowed mode. For the u ′ channel, 10
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