High-Resolution CO and H2 Molecular Line Imaging of a Cometary Globule in the Helix Nebula

We report high-resolution imaging of a prominent cometary globule in the Helix Nebula in the CO J = 1-0 (2.6 mm) and H2 v = 1-0 S(1) (2.12 μm) lines. The observations confirm that globules consist of dense condensations of molecular gas embedded in the ionized nebula. The head of the globule is seen as a peak in the CO emission with an extremely narrow line width (0.5 km s-1) and is outlined by a limb-brightened surface of H2 emission facing the central star and lying within the photoionized halo. The emission from both molecular species extends into the tail region. The presence of this extended molecular emission provides new constraints on the structure of the tails and on the origin and evolution of the globules.