We consider the results of two proton transfer reactions, ${}^{10}\mathrm{B}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^9\mathrm{Be}$ and ${}^{14}\mathrm{N}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^{13}\mathrm{C},$ to obtain a weighted average of the measured asymptotic normalization coefficients for the virtual transition ${}^7\mathrm{Be}+p{\leftrightarrow }^8\mathrm{B}.$ These coefficients specify the amplitude of the tail of the ${}^8\mathrm{B}$ overlap function in the ${}^7\mathrm{Be}+p$ channel, and are used to calculate the astrophysical S factor for the direct capture reaction ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ at solar energies, $S_{17}\mathrm{}\left(0\right).$ In light of recent improvements in the determination of optical-model potentials, including detailed understanding of the correlations between the DWBA analyses of the two experiments, and a new experimental measurement of the asymptotic normalization coefficients for the virtual transition ${}^{13}\mathrm{C}+p{\leftrightarrow }^{14}\mathrm{N},y$ we report a weighted average asymptotic normalization coefficient of $C_{p_{3/2}}^2=0.388\mathrm{}\pm 0.039\hspace{0.5em}{\mathrm{fm}}^{-1}$ for ${}^8\mathrm{B}\mathrm{}{\leftrightarrow }^7\mathrm{Be}+p,$ which implies $S_{17}\mathrm{}\left(0\right)=17.3\mathrm{}\pm 1.8$ eV b.

• Received 29 June 2000

DOI:https://doi.org/10.1103/PhysRevC.63.055803