WEAVE imaging spectroscopy of NGC 6720: an iron bar in the Ring

TL;DR

This study uses WEAVE spectroscopy to reveal a unique iron-rich 'bar' in the Ring Nebula, suggesting localized dust processing and raising questions about its origin and the nebula's internal structure.

Contribution

First spatially resolved spectroscopy of NGC 6720's central region revealing a distinct iron-rich structure not previously observed.

Findings

Discovery of [Fe V] and [Fe VI] emission confined to a narrow central 'bar'

No other elements share this bar-shaped morphology or similar velocity profile

Indications of dust grain destruction in the region, but no evidence of strong shocks or hot gas

Abstract

We present spatially resolved spectroscopic observations of the planetary nebula NGC 6720, the Ring Nebula, taken during the science verification phase of WEAVE, a new instrument mounted on the William Herschel Telescope on La Palma. We use the instrument's Large Integral Field Unit (LIFU) to obtain spectra of the Ring Nebula, covering its entire optically bright inner regions as well as parts of its much fainter outer molecular halo. We report the discovery of emission from [Fe~{\sc v}] and [Fe~{\sc vi}] confined to a narrow ``bar'' extending across the central regions of the nebula. No lines of other elements share this morphology or, at the spectral resolving power used ($R \sim 2500$), the same radial velocity. The extent to which iron in this bar is depleted is presently unclear; comparison with JWST-detected dust continuum emission suggests that some dust grain destruction may be occurring in the region, but there is currently no observational evidence for the $>$ 50~km\,s$^{-1}$ shock waves or $T > 10^6$~K X-ray emitting gas needed to enable this. Where the bar is located along the line of sight through the nebula, and how it was created, are new puzzles to be solved for this iconic planetary nebula.