Detectability limits of possible companions to S106IR, obtained as described in Sect. 3.4. The solid line indicates the closest separation at which a star with a given difference of z′ magnitude with respect to that of S106IR, Δz′, and obscured by the same amount of foreground extinction would still be distinctly detectable at the 3σ level. The dotted lines show the spectral type corresponding to companions with different magnitude differences, and the dashed lines indicate the projected distances corresponding to selected separations at the distance of 1.3 kpc.