departures from the spherical symmetry and spiral-like structures in the inner regions of the envelope ([@dec2015] 2015; [@vel2015] 2015; [@agu2015] 2015; [@qui2016] 2016). The $\sim$1$''$ angular resolution maps (see Fig. \[fig:map\_all\] using white circles as a reference) show that the molecular shell is not exactly centered on the position of the star but shifted by a few arcseconds in the NE direction. It seems as though the shell of carbon chains is compressed from the SW direction, a result that is also observed at larger scales in CO ([@cer2015] 2015). It is currently unclear whether this feature is the result of an enhanced ultraviolet illumination from the direction of the Galactic plane (SW) or it is linked to the non isotropic character of the mass loss process. It is noteworthy that, unlike some of the previous observations at lower angular resolution (see, for example, the case of C$_2$H in [@gue1997] 1997), the maps in Fig. \[fig:map\_all\] show no evidence of axial symmetry.

The structure of thin shells and inter-crossing arcs is common to the emission distribution of the different species studied (at least for those mapped with $\sim$1$''$ angular resolution; see Fig \[fig:map\_all\]). These similarities indicate that the maxima of 