Roche-lobe radius of donor star in IGR J17451−3022 as a function of its mass, M₂ (black solid line), compared to a selection of the measured masses and radii of stars on the MS (blue points). The dashed red line shows the relation of R₂ = R_⊙(M₂/M_⊙)^0.9 for M₂ ≥ 0.1 M_⊙, which approximates the middle of the MS, and R₂ = 0.1 R_⊙ for M₂< 0.1 M_⊙, which approximately describes the case of old brown dwarfs. The green and cyan curves show the models of stars on the ZAMS and TAMS, respectively. The intersections of these curves with the Roche-lobe radius show that MS stars in the mass range of ≃ (0.52−0.84) M_⊙ are acceptable models of the donor star.