Colour–colour diagram showing the possible contaminant sources with K₀ < 14.75 mag discussed in the Sect. 3.1. C- and M-type sources are shown as squares and triangles respectively. The solid diagonal lines show the colour selection criteria applied during this study (J − K)₀ = 0.74 and 1.20 mag. The horizontal line at (J − H)₀ = 0.72 mag shows the position of the foreground colour boundary. The long-dash diagonal line represents the blue J − K boundary of Kacharov et al. (2012) and the dash-dot line the blue-limit of (Bessell & Brett 1988), Sect. 5.3.2. The short-dash horizontal line represents the alternative (J − H)₀ = 0.80 mag colour criterion considered in Sect. 5.3.1.