(a): for comparison, the log-scaled Qphi image is shown again without highlighted features. The tick marks are the same as for Fig. 2. (b): spiral arm overlayed on the deprojected image (log scale) using the non-flaring height profile, with the same feature annotations as used in Fig. 2. The outer green-white-orange spiral (containing features R1 and A2) is a simple Archimedean spiral as described by Eq. (6), while the inner red-white-red dashed line is a mere illustration of how B1 could be connected to the base of the green spiral. The green and orange dashed lines trace the R1 and A2 structures, respectively. The red dashed lines, which trace the inner structures to the southeast and southwest of the star, clearly have different spiral properties than the outer spiral, most notably at the transition from red to green. Although no clear radial peak is detected at the positions of the white dashed lines in both the outer and inner structures, they follow the same behavior as the outer and the inner arms, respectively. Feature A3 is difficult to recognize because it is stretched into a diffuse region outside the white spiral and is not described by any dashed line.