Radius of the Roche lobe around the unseen component. The radius is calculated for sample mass ratios, q, as given by the symbols, for five possible masses of the K giant, assuming r_K = 16 R_⊙ (see text). The solid lines are the radii of an equatorial disc corresponding to the phase coverage of the eclipse, Δϕ = 0.1, colour-coded for the values of q. For q = 0.1 the equatorial disc lies within the Roche lobe, but for increasing values of q the radius of the eclipsing material progressively exceeds the Roche lobe by up to 22% at q = 0.5.