Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-06-26
Astrophys.J.592:L67-L70,2003
Astronomy and Astrophysics
Astrophysics
10 pages, 2 figures, ApJL in press
Scientific paper
10.1086/377681
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.
Ando Hiroyasu
Aoki Wako
Beers Timothy C.
Fujimoto Masayuki Y.
Iwamoto Nobuyuki
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