Maps of the CO(2–1) line emission at the star velocity (–26.5 km s^-1) viewed by the SMA before (left) and after (right inclusion of the 30-m single-dish short spacings. The yellow curve shows the intensity profile along an EW strip passing through the central star. Most of the bright CO arcs have circular shapes and denote the intersection of the meridional plane with thin spherical shells. The latter typically extend over several steradians, as illustrated by the arc at r = 118′′ in the western half of the envelope (dashed yellow circle). The dense gas shell associated with this arc can be followed over π radians along the line of sight in Fig. 19.