Stellar radius of the main component versus the orbital period of the binary system. Colour indicates the eccentricity of the systems (Table 3). Stars from our sample (Tables 1 and 2) are plotted as filled dots. KIC 5006817 is marked with a cross. The eclipsing red giant KIC 8410637 (Hekker et al. 2010; Frandsen et al. 2013) is shown as a triangle. The stars found in the LMC (Nicholls & Wood 2012) are shown as squares. Solid lines show the period of a system with a total mass of 1.8 M_⊙ and a semi-major axis, which is a multiple of the stellar radius.