Improved Laboratory Transition Probabilities for Er II and Application to the Erbium Abundances of the Sun and Five r-Process-rich, Metal-poor Stars

Recent radiative lifetime measurements accurate to ±5% (Stockett et al. 2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 7 even-parity and 63 odd-parity levels of Er II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 418 lines of Er II. This work moves Er II onto the growing list of rare-earth spectra with extensive and accurate modern transition probability measurements using LIF plus FTS data. This improved laboratory data set has been used to determine a new solar photospheric Er abundance, log ɛ = 0.96 +/- 0.03 (σ = 0.06 from 8 lines), a value in excellent agreement with the recommended meteoritic abundance, log ɛ = 0.95 +/- 0.03. Revised Er abundances have also been derived for the r-process-rich metal-poor giant stars CS 22892-052, BD +17 3248, HD 221170, HD 115444, and CS 31082-001. For these five stars the average Er/Eu abundance ratio, langlelog ɛ (Er/Eu)rangle = 0.42, is in very good agreement with the solar-system r-process ratio. This study has further strengthened the finding that r-process nucleosynthesis in the early Galaxy, which enriched these metal-poor stars, yielded a very similar pattern to the r-process, which enriched later stars including the Sun.