Niobium and rubidium in the barium star zeta Capricorni.

An abundance analysis of the elements Rb to Nb (relative to the G-giant standard ɛ Vir) has been carried out for the barium star ζ Cap using low-noise, high-resolution Digicon and Reticon spectra. Tech's (1971) low abundance of Nb in ζ Cap suggests that the s-process ceased less than about a million years ago. The authors' improved analysis finds a higher Nb abundance consistent with the complete decay of ⁹³Zr to ⁹³Nb; i.e., more than 3×10⁶ years have elapsed since the principal phase of s-processing. The abundance of Rb suggests a neutron density of N(n) ≡ 10⁷cm^-3 for the s-process site at the close of s-processing.