Illustration of the disk emission subtraction in the northern hemisphere. Left panel: ¹²CO emission of HH30 at 9.6 km s⁻¹ before subtraction of the disk contribution. Right panel: same channel after subtraction of the southern emission (blue rectangle on the left panel) from the northern emission (red rectangle on the left panel). The black contours show the +3σ, +5σ, and +7σ levels, while the red contours outline negative contours at −3σ, −5σ, and −7σ with σ = 2.0 mJy beam⁻¹ km s⁻¹.