VLA observations of NH3 and HC7 N in the EGG Nebula (CRL 2688) : the shell kinematics.

The authors have used the VLA to map the Egg Nebula in the inversion line (1, 1) of NH₃ and the rotation line J = 21-20 of HC₇N, simultaneously. Besides the determination of the geometry of the circumstellar shells in both transitions, the interferometric observations have also revealed that the kinematics of the molecular shells departs from a pure expansion. Most of the NH₃ emission arises in a disk and more probably a toroid oriented almost edge-on and lying along the dark lane separating the two optical lobes. The infrared object is located at the centre of the NH₃ disk. The HC₇N shell which is probably an oblate spheroid appears as a halo surrounding the infrared source and extends beyond the optical lobes. The strong asymmetry observed in the NH₃ spectra and position-velocity maps can be attributed to an anisotropic blueshifted motion similar to a bipolar flow originating from the central infrared object.