Comparison of the north (top) and south (middle) parts of the disk for 2019-03 ADI (left) and 2019-06 PDI IRDIS (right) observations obtained in K band. The NW spiral trace corresponds to the one measured on the ADI data set, following the method presented in Sect. 3.1. The SE trace corresponds to the symmetric arm trace relative to the semimajor axis of the inclined disk plane, using the (Keppler et al. 2019) disk parameters. The relative flux displayed in the bottom panels was computed on a four-pixel aperture. Each point is weighted by the flux measured in the disk at the same angle coordinate. The disk ellipse (dashed line) was computed to fit the local maxima found on the ADI image. The red and blue x-axis labels in the relative flux panel correspond respectively to the position of the NW arm trace relative to the star, and to the position of its SE symmetric.