Bolometric correction at 3.6 μm vs. [3.6]−[8.0] colour (left) and K vs. J−K colour (right) for C stars (top panels) and M stars (bottom panels). The solid dark-blue lines are polynomial fits to the data (see Table 2). See Sect. 5.2 for an explanation of sources not fitted or plotted. For C stars in the top right panel, red stars indicate models by Nowotny et al. (2013), green dots indicate models by Eriksson (2014), the dotted red line indicates the fit by Kerschbaum et al. (2010), and the dashed red line indicates the fit by Whitelock et al. (2006). For M stars in the lower-right panel, the straight red lines indicate relations “A”, “B”, and “C” from Kerschbaum et al. (2010), valid in the range 1.0 <J−K< 1.6, 1.1 <J−K< 1.95, and 1.75 <J−K< 2.9 mag, respectively. The dashed light blue line indicates the fit by WBF.