Free–free characteristics of the sample. (a) Comparison of theoretically predicted mass-loss rates (﹩\dot{{M}_{{\rm{th}}}}﹩) and mass-loss rate assuming a completely free–free thermal emission (﹩\dot{{M}_{{\rm{ff}}}}﹩). The black solid line represents ﹩\dot{{M}_{{\rm{th}}}}=\dot{{M}_{{\rm{ff}}}}﹩, while the dashed line represents ﹩\dot{{M}_{{\rm{ff}}}}=1{0}^{4}\dot{{M}_{{\rm{th}}}}﹩. (b) Variation of the ratio of free–free radius R_ff and Alfvén radius R_A with effective temperature. The black dashed horizontal line represents the R_ff = R_A boundary. For stars with R_ff > R_A, the effect of FFA is predicted to be significant. For both figures, the symbols are the same as in Figure 4, with uniform symbol size.