Three composite images showing the distribution of different atoms, ions, and molecules along the western rims of the Helix nebula. a) [N ii] at 1461 GHz in red, CO (J = 5–4) in green. Yellow areas are the regions where [N ii] emission coincides with CO (J = 5–4) emission. b) CO (J = 5–4) in green and OH⁺ in blue. c) CO (J = 5–4) in green and [C i] (–) in blue. Cyan areas are the regions where CO (J = 5–4) emission coincides with the OH⁺ emission in b), and with the [C i] emission in c). White contours trace the H₂ distribution on the H₂ 2.122 μm map.