Initial masses of W UMa type contact binaries

We discover that the A- and the W-subtype contact binaries have different ranges of initial secondary masses. Binary systems with an initial mass higher than 1.8+/-0.1M_{sun}_ become A-subtype while systems with initial masses lower than this become W-subtype. Only 6 per cent of systems violate this behaviour.

We also obtain the initial masses of the primaries using the following constraint for the reciprocal of the initial mass ratio: 0<1/q_i_<1. The range of initial masses we find for the primaries is 0.2-1.5M_{sun}_, except for two systems. Finally in comparing our models to observed systems, we find evidence that the mass transfer process is not conservative.

We find that only 34 per cent of the mass from the secondary is transferred to the primary. The remainder is lost from the system.