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Annotatsiya
We point out a simple relation between the nuclear vertex constant (NVC) and the overall normalization of the astrophysical $S$ factor. Using predicted values of the NVC for the virtual decay of $^{8}\mathrm{B}\ensuremath{\rightarrow}^{7}\mathrm{Be}+p$ we find ${S}_{17}(0)\ensuremath{\approx}17.6$ eVb for $^{7}\mathrm{Be}{(p,\ensuremath{\gamma})}^{8}\mathrm{B}$ reactions, consistent with the low values extrapolated from direct capture measurements by Filippone et al. and by Vaughn et al. New possibilities, using proton transfer reactions, to measure the astrophysical $S$ factor indirectly are proposed.