Stellar evolution tracks computed using the Heger et al. (2000) stellar evolution program with mass M = 4.21   M_⊙, convective core overshooting with α_c = 0.2 and varying values of the helium abundance, Y, and metallicity, Z. The Heger et al. (2000) code assumes the values of Y and Z to be correlated, such that dY/dZ = 2. The red solid line represents Y,Z = 0.250,0.005, green dashed line 0.256,0.008, blue small-dashed line 0.264,0.012 and the magenta dotted line is 0.270,0.015. The black triangles with error bars represent the observed radius and effective temperature of the binary components.