Evolution of orbital period, eccentricity, and released accretion energy of a selected binary model as a function of the mass of the optical companion. Time evolution proceeds from left to right. Light-blue regions represent observational constraints with increased error bars (see Sect. 4). The x-axis corresponds to possible matching values for Wray 977, which is thought to be above 33 M_⊙ (Kaper et al. 2006).