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

TL;DR

This paper presents detailed JWST imaging of the Ring Nebula, revealing its complex structure, globules, and arcs, and discusses the nebula's morphology, stellar companions, and possible formation mechanisms.

Contribution

First JWST imaging study of NGC 6720 that uncovers detailed nebular structures, globules, and stellar companions, providing new insights into its morphology and formation.

Findings

The nebula contains ~20,000 dense globules with high density.

Presence of concentric arc-like features suggests orbital modulation by a low-mass companion.

The central star is part of a triple system with a wide M dwarf companion.

Abstract

We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6$\mu$m to 25 $\mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H$_2$, with a characteristic diameter of 0.2 arcsec and density $n_{\rm H} \sim 10^5$-$10^6$ cm$^{-3}$. The shell contains a thin ring of polycyclic aromatic hydrocarbon (PAH) emission. H$_2$ is found throughout the shell and in the halo. H$_2$ in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is shown to be filled with high ionization gas and shows two linear structures. 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 are shown which reproduce the clumping and possibly the spikes. Around ten 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. The system is therefore a triple star. 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.