Relation between X-ray (0.517–12.4 nm) and EUV (10–36 nm) surface fluxes, F_X and F_EUV, for the sample of stars given in Table 3. The colours and sizes of the circles represent spectral type and mass and the yellow region and the inset shows the Sun at different times during the solar cycle. The open red circle shows the M dwarf GJ 832, with fluxes derived from the stellar parameters and semi-empirical model spectrum of Fontenla et al. (2016).