To start the calculations, we choose the distributions of initial binary parameters: mass of the primary ZAMS component, ; binary mass ratio, ; and orbital separation, a. Initial eccentricity is assumed to be zero.
The distribution in orbital separations is taken as deduced from observations (Abt 1983):
As for the mass ratio distribution in binaries, the observational information is poor. Meanwhile, from the evolutionary point of view, it is particularly important how different are the initial masses of the components (see, e.g., Trimble 1983). A customary `zero assumption' is that the mass ratio distribution has a flat shape, i.e. the binaries with a high mass ratio occur as frequently as those with equal masses. As one cannot reliably establish such distribution directly from observations (due to a number of selection effects), we have parametrized it by a power law, assuming the primary mass distribution to obey the Salpeter mass function:
A comparison of the observed X-ray source statistics with the predictions of the current evolutionary scenarios shows (Lipunov et al. 1995b) that the initial mass ratio should be strongly centered around unity, so that we assume in the present calculations.