The Molecular Envelope of the Helix Nebula

We present a fully sampled map of the Helix Nebula in the 1.3 mm CO J = 2-1 line, made using the Caltech Submillimeter Observatory. The angular resolution is 31'', and the velocity resolution is 1.5 km s-1. The CO emission is found to extend over a region ~1000'' × 800'' and delineates the well-known double ring or "helix" seen in optical images of the ionized gas. Our observations provide the first complete view of the global kinematics of the envelope and reveal the three-dimensional structure of the gas. The helix is seen to be an expanding, equatorial ring around the ionized nebula, with arcs extending to higher latitudes and exhibiting remarkable point symmetries about the central star. The molecular gas is fragmented into many small condensations with narrow line widths (~1 km s-1). The close relationship found between the structure of the envelope and the ionized nebula underscores the important role of neutral gas in determining the morphology of planetary nebulae. The point symmetries provide evidence for early shaping of the envelope by bipolar outflows or jets.