Investigating the haloes of planetary nebulae – IV. NGC 6720, the Ring Nebula

New spatially resolved spectral observations taken at high wavelength resolution have been obtained of the Ring Nebula using the Manchester Echelle Spectrometer combined with the Isaac Newton Telescope on La Palma. This planetary nebula has long been thought to have a non-spherical bright nebular core. The new observations show conclusively that the limb-brightened, faint inner halo which surrounds the bright nebular core cannot have the form of a radially expanding, spheroidal shell, but rather must be bipolar in nature. The observed [N II] 6584-Å emission line profiles are clearly split into two components, separated by $$\sim 30\ {\rm km}\ {\rm s}^{-1}$$ at all observed points on this inner halo. A new model for the Ring Nebula is postulated in the light of the new spectral data. The very faint outer halo is thought to be the remnants of the original red giant wind. This wind contained an equatorial density enhancement which confined the superwind ejection into two oppositely inclined lobes, which are observed almost end on. The [N II] 6584-Åemission was found to be particularly strong in the limb-brightened outer rim of the inner halo, being about 1.5 times stronger than the $${\rm H}\alpha$$ emission from the same region.