A. J. Gallagher, S. G. Ryan, A. Hosford, A. E. Garcia Perez, W. Aoki, S. Honda
We provide measurements of the Ba isotopic fractions for five metal-poor
stars derived with an LTE analysis using 1D model stellar atmospheres. We use
high resolution (R\equiv{\lambda}/\Delta{\lambda}=90000-95000), very high
signal-to-noise (S/N>500) spectra to determine the fraction of odd Ba isotopes
(fodd) by measuring subtle asymmetries in the profile of the Ba ii line at 4554
{\AA}. We also use two different macroturbulent broadening techniques, Gaussian
and radial-tangential, to model the Fe lines of each star, and propagate each
technique to model macroturbulent broadening in the Ba 4554 {\AA} line. We
conduct a 1D non-LTE (NLTE) treatment of the Fe lines in the red giant HD122563
and the subgiant HD140283 in an attempt to improve the fitting. We determine
[Ba/Eu] ratios for the two giants in our study, HD122563 and HD88609, which can
also be used to determine the relative contribution of the s- and r-processes
to heavy-element nucleosynthesis, for comparison with fodd. We find fodd for
HD122563, HD88609 and HD84937, BD+26\circ3578 and BD-04\circ3208 to be
-0.12\pm0.07, -0.02\pm0.09, and -0.05\pm0.11, 0.08\pm0.08 and 0.18\pm0.08
respectively. This means that all stars examined here show isotopic fractions
more compatible with an s-process dominated composition. The [Ba/Eu] ratios in
HD122563 and HD88609 are found to be -0.20\pm0.15 and -0.47\pm0.15
respectively, which indicate instead an r-process signature. We report a better
statistical fit to the majority of Fe profiles in each star when employing a
radial-tangential broadening technique during our 1D LTE investigation. We have
shown that, from a statistical point of view, one must consider using a
radial-tangential broadening technique rather than a Gaussian one to model Fe
line macroturbulences when working in 1D. No improvement to Fe line fitting is
seen when employing a NLTE treatment.
View original:
http://arxiv.org/abs/1201.1757
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