Near- to mid-infrared colour − colour diagrams for the same sources as plotted in Fig. 9. Top panel: a J − K_S vs. K_S-S9W colour − colour diagram (Takita et al. 2010) for all sources found in the one-square-degree field with valid near-IR fluxes in the 2MASS catalogue and 9 μm fluxes in the AKARI/IRC catalogue (Fig. 1). The arrow shows the interstellar extinction vector estimated from the Weingartner & Draine (2001) Milky Way model for R_V = 3.1. Dashed-line and solid-line parallelograms show the distribution of CTTSs in the Taurus-Auriga region (Takita et al. 2010) and the distribution of driving sources in our region, respectively. Bottom panel: a J − K_S vs. K_S-L18W colour − colour diagram similar to the top panel, but for sources with valid JHK_S fluxes in the 2MASS catalogue and 18 μm fluxes in the AKARI/IRC catalogue. Colour-bars and symbol sizes indicate the magnitude of the spectral slope (α).