Radiation evolution of two solar mass stars in tight binary systems with different initial orbital separations. In each system, the two stars start with very different initial rotation rates, with red and blue indicating the tracks for slow and fast rotators respectively. The initial orbital separations are written in the bottom left of each panel. The evolutionary tracks end when the two stars merge due to the removal of angular momentum in the stellar wind. The evolutionary tracks that these stars would follow in single systems are shown as dotted lines. The black dotted line shows the saturation XUV luminosity.