Schematic outline of the potential environment of MonR2 IRS 3 where an expanding shell of gas is traced by different molecules at different wavelengths. The individual (yet to be observed) disks of MonR2 IRS 3A, MonR2 IRS 3B and MonR2 IRS 3C are given in yellow. The infrared reflection nebulae extending from MonR2 IRS 3 A are shown in black (Preibisch et al. 2002; Monnier et al. 2009). Scattering of continuum photons from MonR2 IRS 3A at 3 µm may produce the red-shifted HCN emission seen from the red side of an expanding shell, which is also evident in CO emission at 4.67 µm. The blue-side of the shell expanding towards the observer is only seen in CO absorption at infrared wavelengths, which is further away from the star and hence cooler. This side is also evident from HCN 3–2 emission at sub-mm wavelengths (Fuente et al. 2021). In this figure east is left and north is up.