  Astrophysical S-factors at zero energy for the direct nuclear capture
reactions $^{3}{\rm He}(\alpha, \gamma)^{7}{\rm Be}$, $^{3}{\rm H}(\alpha,
\gamma)^{7}{\rm Li}$ and $^{7}{\rm Be}(p, \gamma)^{8}{\rm B}$ are estimated
within the framework of two-body potential cluster model on the basis of
extranuclear capture approximation of D. Baye and E. Brainis. The values of
S(0)-factors have been calculated using two different potential models for each
process, which were adjusted to the binding energies and empirical values of
the asymptotical normalization coefficients from the literature. New values of
S(0)-factors have been obtained.
