Velocity vs. position plot along the equatorial direction (PA 103°) of the Red Rectangle nebula for H¹³CN J = 4−3 (left panel) and H₂O ν₂ = 2 J_Ka, Kc = 3_2, 1–4_1, 4 (right panel). The velocity resolution is 1 km s⁻¹ and the mean spatial resolution is 53 mas (see Sect. 2.1). Contours are −2 (red) and +2 to +10 by +2 (black) mJy beam⁻¹; 1 mJy beam⁻¹ is equivalent to 3.6 K. The adopted LSR systemic velocity (−0.25 km s⁻¹) and center of the nebula (continuum peak) are indicated by the red lines.