¹²CO(2–1) emission towards the center of the VLA1623 envelope. Significant CO (above the 10σ level) emission, associated with the continuum source Knot-A, is detected. a, b) Show the peak spectrum towards VLA1623 and the peak spectrum of the emission feature associated with Knot-A, respectively. In all panels, the central black dotted vertical line indicates the systemic velocity v_LSR ~ 3.8 km s^-1, while the colored dashed vertical lines show the positions of the redshifted and blueshifted components seen in the ¹²CO(2–1) single-dish spectrum towards VLA1623 (André et al. 1990; Dent et al. 1995). c) Shows the 1.3-mm continuum emission map, and contours of ¹²CO(2–1) integrated emission: blueshifted from  − 6 km s^-1 to  + 3.0 km s^-1, redshifted from  +4.5 km s^-1 to  +10 km s^-1. The rms noise in the integrated CO emission map is σ ~ 0.15 Jy/beam km s^-1, and the contours shown are levels of 3-σ to 11-σ by 3-σ ( − 3σ dashed contours). The black crosses and the white squares mark the positions of the continuum sources at 2.7-mm (Looney et al. 2000) and 7-mm (Ward-Thompson et al. 2011), respectively. d) Shows the CO spectrum, integrated over a 3″ box, including the whole extent of continuum emission from both VLA1623 and Knot-A.