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Fig. 3
Images of NGC 7009 in H and He emission line images: H+ as sampled by Balmer 4–2 Hβ 4861.3 Å fromboth the 10 s and 120 s cubes; He+ from the triplet (2P 3d – 3D 2s) He I 5875.6 Å line (120 s cube); and He++ from He II 5411.5 Å 7–4 line (120 s cube).
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