Simulated semi-amplitude (K) velocities for an 8 M_⊙ RSG in a binary system for a range of periods and mass ratios. Coloured solid lines illustrate constant velocities at 2, 5, 10, 15, 20, 30 km s⁻¹, from shallow to steep, respectively. The black dashed line highlights the minimum possible period for an 8 M_⊙ RSG for the corresponding mass ratio assuming that its maximum radius is 400 R_⊙ (Brott et al. 2011). Therefore, all systems to the left of this line are excluded as a result of the size of the RSG primary.