PN line emission. The first four panels show the spectra of the J = 4–3, …, 7–6 transitions;the bottom panel shows the peak-normalised result of stacking these at a velocity resolution of 1.5 km s⁻¹, weighted with the upper level statistical weights, 2J + 1 of the respective transitions. Red lines indicate the rest frequency (or v = 0 km s⁻¹ in the bottom panel) of each transition, blue lines indicate velocities ± 6 km s⁻¹ with respect to the stellar v_LSR. The red curve in the bottom panel represents a Gaussian fit to the stacked data.