Effect of mass ratio on the RV semi-amplitude K of the RG component. The x-axis is the orbital period P_orb expressed in days, which runs from 0.1 day to ≈274 years. The y-axis is the RG mass M₁. Systems are assumed to have a zero eccentricity (e = 0) and to be seen edge-on (i = 90°). Orbital periods P_orb are considered from 0.1 to 100 000 days (≈274 years), and the RG mass M₁ from 0.1 to 5 M_⊙. Top panel: with a mass ratio q = 1; bottom: with q = 0.1. The area delimited by dashed lines indicates the range of values met for systems in which surface activity is measured.