PA = 45$^\circ$ from the maps of the cyanides CN, C$_3$N, HC$_3$N, and HC$_5$N shown in Fig. \[fig:map\_all\]. There are several aspects that are worthy of comment. First, the brightness distributions along the strip selected are not symmetrical with respect to the position of the star, indicating that the circumstellar shells are not strictly concentric, but instead consist of intersecting arcs and a spiral-like structure. Second, if we focus on the SW direction (positive values along $x$-axis), there are several shells of width $\sim$2$''$ at approximately +11$''$, $+15{\mbox{\rlap{.}$''$}}5$, $+21{\mbox{\rlap{.}$''$}}5$, and +27$''$ from the star. These shells are however not traced by the four species. The shells at +$15{\mbox{\rlap{.}$''$}}5$ and +$21{\mbox{\rlap{.}$''$}}5$ are seen in the four species. The shell at +11$''$ is traced by the cyanopolyynes HC$_3$N and HC$_5$N, but not by the radicals C$_3$N and CN, and the farthest one at +27$''$ is mostly seen in CN and to a lesser extent in the cyanopolyynes. Therefore, among the four cyanides, the cyanopolyynes appear at shorter radii than their radicals, while the radical CN is the one that extends farther in the envelope.

![Radial brightness distributions of the hydrocarbon radicals C$_2$H, C$_4$H, and C$_6$H, and of the cyanides CN, HC$_3$N, HC$_5$N, 