Left upper panel: deuterium fraction depending on the molecular hydrogen column density, N(H₂). Right upper panel: deuterium fraction as a function of dust temperature taken from Pattle et al. (2015), Friesen et al. (2009), and Motte et al. (1998). Left lower panel: CO depletion factor versus the molecular hydrogen column density. Right lower panel: CO depletion factor as a function of dust temperature. The protostellar cores are depicted with black open circles; the color coding is given in Fig. 11.