Europium Isotope Ratios in s-Process-Element-Enhanced, Metal-Poor Stars: A New Probe of the 151Sm Branching

Wako Aoki; Sean G. Ryan; Nobuyuki Iwamoto; Timothy C. Beers; John E. Norris; Hiroyasu Ando; Toshitaka Kajino; Grant J. Mathews; Masayuki Y. Fujimoto

doi:10.1086/377681

arXiv · astro-ph/0306544

Europium Isotope Ratios in s-Process-Element-Enhanced, Metal-Poor Stars: A New Probe of the 151Sm Branching

Wako Aoki·Sean G. Ryan·Nobuyuki Iwamoto·Timothy C. Beers·John E. Norris·Hiroyasu Ando·Toshitaka Kajino·Grant J. Mathews·Masayuki Y. Fujimoto

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Abstract

We report on the first measurement of the Eu isotope fractions (151Eu and 153Eu) in s-process-element-enhanced, metal-poor stars. We use these ratios to investigate the 151Sm branching of s-process nucleosynthesis. The measurement was made by detailed study of Eu II lines that are significantly affected by hyperfine splitting and isotope shifts in spectra of the carbon-rich, very metal-poor stars LP625-44 and CS31062-050, observed with the Subaru Telescope High Dispersion Spectrograph. The 151Eu fractions [fr(151Eu) = 151Eu/(151Eu+153Eu)] derived for LP625-44 and CS31062-050 are 0.60 and 0.55, respectively, with uncertainties of about +/- 0.05. These values are higher than found in solar-system material, but agree well with the predictions of recent s-process models. We derive new constraints on the temperature and neutron density during the s-process based on calculations of pulsed s-process models for the 151Eu fraction.

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Wako Aoki, Sean G. Ryan, Nobuyuki Iwamoto, Timothy C. Beers, John E. Norris, Hiroyasu Ando, Toshitaka Kajino, Grant J. Mathews, Masayuki Y. Fujimoto. 2003-06-26. Europium Isotope Ratios in s-Process-Element-Enhanced, Metal-Poor Stars: A New Probe of the 151Sm Branching. https://doi.org/10.1086/377681

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