AAS Meeting #193 - Austin, Texas, January 1999
Session 15. Planetary Nebulae
Display, Wednesday, January 6, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[15.08] Unwinding the Helix

P.J. Huggins (NYU), K. Young (SAO), P. Cox (IAS, Paris), T. Forveille (Obs. de Grenoble), R. Bachiller (OAN, Madrid)

We present new observations of the Helix nebula (NGC 7293) which reveal its large scale, 3-dimensional structure. The Helix probably ranks as the best known planetary nebula, and the apparent form of a double ring or helix is familiar from many published optical images of the nebula. The true structure has, however, long been an open question, and in this paper we present a new approach to this problem. Using the 10.4~m telescope of the Caltech Sub-millimeter Observatory we have mapped the entire (\approx 1000 \arcsec) Helix in the 1.3~mm CO J= 2-1 line, with an angular resolution of ~30\arcsec and a velocity resolution of 1.5~km\,s-1. The CO emission indicates the presence of a massive neutral envelope in the Helix, which exhibits the apparent ring structure seen in optical images. It evidently forms a reservoir of neutral gas for the formation of the nebula and dictates the shape of the newly ionized gas. From the detailed kinematics of the envelope we have reconstructed the 3-dimensional shape, based on homologous expansion. Views of the envelope are presented using 3-dimensional visualization techniques. These views reveal the structure of the Helix, and its appearance as seen from different directions in space.


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