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First Stars III
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Poster
Title: Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars Author(s): Ian Roederer Abstract: We have derived isotopic fractions of europium (Eu), samarium (Sm), and neodymium (Nd) in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new very high resolution (R ~ 120,000), high signal-to-noise (S/N ~ 160-1000) spectra obtained with the 2dCoude spectrograph of McDonald Observatory's 2.7m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. Our resulting isotopic fraction estimates argue for an r-process origin for the rare-earth elements in HD 175305 and an s-process orgin for them in HD 196944, in excellent agreement with previous studies of the elemental abundance distributions in these stars. This study for the first time extends the n-capture origin of multiple rare earths in metal-poor stars from elemental abundances to the isotopic level, greatly strengthening the r-process interpretation for HD 175305 and the s-process interpretation for HD 196944.
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