Line proflies from the ¹²CO and ¹³CO v = 1–0 band at 4.67 µm in the atmospheric M band (Lee et al., in prep.). The ¹²CO P(14), ¹³CO R(13) and ¹²CO P(26) lines are shown panels a, b and c respectively. The profiles in black and red originate from the 3A and 3B binary sources respectively. The dashed denotes the cloud velocity at 10 km s−1. The P Cygni profile is most obvious in the P(14) profile of the MonR2 IRS 3A source but actually present in all lines (Lee et al., in prep.).