Q_φ image (panel a) and isophotal contours of polarized light intensity overlying the Q_φ image (panelb). The original data (OBS177_0010-0042) were 6 × 6 binned to highlight the disk shape and to reduce the photon noise level. The position of the star is indicated by a yellow asterisk. White brackets in the top panel show the boundaries of two rectangular areas where the counts were summed up to retrieve the total polarized flux of the disk (see Sect. 5.3). Image (panel b) is smoothed via a Gaussian kernel with σ_kernel = 3 px. The isophotal contours show levels of the surface brightness with approximately 25, 40, and 50 counts per binned pixel (from the lowest to the highest contour). Arrows “A” and “B” mark the location of the increased surface brightness, which could indicate the radius of the planetesimal belt. The x-axis coincides with the disk axis at estimated PA θ_disk = 112° (see Sect. 5). The color bar shows the surface brightness in counts per binned pixel.