An illustrative set of 8 individual WEAVE LIFU emission-line images of the Ring Nebula (IMAGE)
Caption
Figure 2: An illustrative set of 8 individual WEAVE LIFU emission-line images of the Ring Nebula. The colour in each panel tracks the brightness of emission, with brown-red being the most intense, shading through yellow and green to blue for the faintest emission. North is up and east, left.
The 4 emission line images that are combined in Figure 1 are shown separately in the top row. Left to right, the emission lines are: the [Fe V] 4227 Angstrom (422.7 nm) line due to four-times-ionized iron atoms; the [O I] 6300 Angstrom auroral line due to neutral oxygen atoms; the [O II] 3727 Angstrom line pair due to singly-ionized oxygen atoms; the [O III] 4959 Angstrom line due to twice-ionized oxygen atoms.
Bottom row, from left to right: emission in the 4861-Angstrom line that is produced as ionized hydrogen atoms recombine in the nebula; emission in the [N II] 6548 Angstrom line of singly-ionized nitrogen; emission in the C II 4267 Angstrom line resulting from the recombination of twice-ionized carbon atoms; emission in the [Ar V] 6435 Angstrom line by four-times-ionized argon.
Notice the very different appearance of the emission from four times ionized iron atoms (top left) compared to the emission from four-times-ionized argon atoms (bottom right) – usually, these ions of argon and iron arise in the same volume, as they require the same physical conditions.
The angular dimensions of each of the 8 frames are 120 x 110 arcseconds on the sky (E-W x N-S), corresponding to physical dimensions of 95,000 x 87,000 Astronomical Units (AU) at the 787 parsec distance of the Ring Nebula. An Astronomical Unit is the mean distance from the Sun to the Earth.
Credit
R. Wesson, Cardiff University/UCL
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