Fig. 3. Lower limit to the initial semi-major axis at which the binary survives the spiral-in, as function of the initial mass of the primary, calculated with use of the evolutionary sequences by Schaller et al. (1992). The upper (lower) dashed line gives the limit determined from the condition that the secondary star (helium core) is smaller than its Roche-lobe, The solid line gives the upper limit at which the primary reaches its Roche lobe at its maximum radius of . The secondary is assumed to be a 1  star. The dotted line indicates the initial semi-major axis of a binary in which a 1  secondary can fill its Roche lobe after the primary has lost its entire envelope without ever having filled its Roche lobe