The J = 2 − 1 line of CO at 230,538.000 MHz observed in T Mic in the compact configuration. The plots show how (in the example of T Mic) the velocity (v_max) was derived from the molecular lines observed in the ATOMIUM survey. Left: The CO spectra extracted with apertures of radius 0.6″ (blue), 1.8″ (red), and 5.4″ (green). Right: The CO profile extracted with an aperture of radius 2.06″ is plotted on an expanded flux density scale with a full scale amplitude of 0.4 Jy/beam to better discern the red and blue wings. The horizontal dashed grey line at 5 mJy beam⁻¹ corresponds to the 1σ peak rms noise (see point #2 in Sect. 5.2); the horizontal dotted grey line at 15 mJy beam⁻¹ corresponds to the 3σ peak rms noise; the green dotted vertical line denotes the line center of CO at the v_LSR of +25.5 km/sec; and the red dashed vertical lines indicate the blue wing velocity of −12.7 km s⁻¹, and the red wing velocity of 8.9 km s⁻¹. The value of v_max(CO) with the largest magnitude – i.e., the blue wing velocity of 12.7 km s⁻¹ – is designated as the ‘velocity measure’ of the CO J = 2 − 1 transition in T Mic (see Sect. 5.2). Similarly, the dashed green horizontal line at 76 mJy beam⁻¹ corresponds to the 1σ_rms noise in the Band 6 spectrum of CO observed in T Mic by Ramstedt et al. (2020, see Table B.1). The dotted green horizontal line at 228 mJy beam⁻¹ corresponds to the 3σ_rms noise and to the point where the full width of the CO J = 2 − 1 line profile is equal to 12.5 km s⁻¹, whereby Ramstedt et al. determined v_max(CO) = 6.25 km s⁻¹.