large separation in the science images. [This non-optimal sky subtraction can affect the accuracy of the background subtraction to values below $\sim$8% for the IRDIS RDI images, which are used [to measure]{} the disk photometry]{} (Sect. \[sec:disk\]). All the other calibration data (darks, detector flats, wavelength calibration, IFU flats) were obtained during the following day.

Data reduction and analysis {#sec:datareduc}
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The data were reduced with the SPHERE Data Center pipeline, which uses the Data Reduction and Handling software [v0.15.0, @Pavlov2008] and dedicated IDL routines for the IFS data reduction [@Mesa2015]. The pipeline subtracts the sky background, corrects for the detector flat field, removes bad pixels, derives the IFS wavelength calibration, corrects for the IFU [flat, corrects]{} for anamorphism [0.60$\pm$0.02%, @Maire2016a], and registers the frames using the coronagraphic images taken with the satellite spots. We measured the full width at half maximum of the point-spread function (PSF) for the IRDIS images to be $\sim$56 mas ($K1$) and $\sim$59 mas ($K2$) and for the IFS images to be $\sim$37 mas ($J$) and $\sim$42 mas ($H$)[^5]. Then, the data were analyzed with a consortium image processing pipeline (R. Galicher, private comm.). This pipeline allows for several imaging post-processing techniques: classical angular differential 