The molecular envelope of NGC 7027

We present maps of the J = 1-0 emission line of CO toward the planetary nebula NGC 7027. The images were made by combining interferometer observations from the Berkeley-Illinois-Maryland Array (BIMA) with single-dish observations from the NRAO 12 m telescope. The maps have an angular resolution of 5″ and contain all the flux in the CO J = 1-0 line. The integrated intensity map shows that the circumstellar molecular envelope has a diameter to zero intensity of ∼70″, corresponding to a linear size of 0.30 pc at distance of 900 pc. The envelope has an axisymmetric, clumpy appearance, with unresolved clumps having a size of <0.02 pc. Maps at the line center reveal a bright inner ring of CO emission which surrounds a central CO minimum coincident with the ionized gas. The neutral envelope possesses axial symmetry which is aligned with the symmetry axis of the ionized nebula. The expansion of the molecular gas is evident in position-velocity maps, especially along the symmetry axis (P.A. 150°), and in the orthogonal direction. The morphology of the CO emission implies that (1) the molecular material is constraining the development of the ionized nebula; (2) mass loss from the central star was neither spherically symmetric nor completely uniform in time; and (3) the molecular envelope contains significant structure on scales smaller than 5″.