The barium isotopic fractions in five metal-poor stars

TL;DR

This study measures barium isotopic fractions in five metal-poor stars using high-resolution spectra and compares different broadening techniques, revealing s-process dominance in isotopic composition despite r-process signatures in certain abundance ratios.

Contribution

It provides new Ba isotopic fraction measurements in metal-poor stars and demonstrates the effectiveness of radial-tangential broadening over Gaussian in spectral line modeling.

Findings

All stars show isotopic fractions consistent with s-process dominance.

Radial-tangential broadening yields better spectral fits than Gaussian.

NLTE treatment does not improve Fe line fitting.

Abstract

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.