JWST observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs

Wesson, R.; Matsuura, Mikako; Zijlstra, Albert A.; Volk, Kevin; Kavanagh, Patrick J.; García-Segura, Guillermo; McDonald, I.; Sahai, Raghvendra; Barlow, M. J.; Cox, Nick L. J.; Bernard-Salas, Jeronimo; Aleman, Isabel; Cami, Jan; Clark, Nicholas; Dinerstein, Harriet L.; Justtanont, K.; Kaplan, Kyle F.; Manchado, A.; Peeters, Els; Van de Steene, Griet C.; van Hoof, Peter A. M.
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Monthly Notices of the Royal Astronomical Society

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We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6 to 25 $\, \mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H2, with a characteristic diameter of 0.2 arcsec and density nH ~ 105-106 cm-3. The shell contains a narrow ring of polycyclic aromatic hydrocarbon (PAH) emission. H2 is found throughout the shell and also in the halo. H2 in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is filled with high-ionization gas and shows two linear structures which we suggest are the edges of a biconal flow, seen in projection against the cavity. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features ('spikes') extend outward from the ring, pointing away from the central star. Hydrodynamical simulations reproduce the clumping and possibly the spikes. Around 10 low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2-M4 dwarf. NGC 6720 is therefore a triple star system. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae.