Jin Ren, Norbert Christlieb, Gang Zhao
We report thorium abundances for 77 metal-poor stars in the metallicity range
of -3.5<[Fe/H]}<-1.0, based on "snapshot" spectra obtained with VLT-UT2/UVES
during the HERES Survey. We were able to determine the thorium abundances with
better than 1-sigma confidence for 17 stars, while for 60 stars we derived
upper limits. For five stars common with previous studies, our results were in
good agreement with the literature results. The thorium abundances span a wide
range of about 4.0 dex, and scatter exists in the distribution of log(Th/Eu)
ratios for lower metallicity stars, supporting previous studies suggesting the
r-process is not universal. We derived ages from the log(Th/Eu) ratios for 12
stars, resulting in large scattered ages, and two stars with significant
enhancement of Th relative to Eu are found, indicating the "actinide boost"
does not seem to be a rare phenomenon and thus highlighting the risk in using
log(Th/Eu) to derive stellar ages.
View original:
http://arxiv.org/abs/1112.4870
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