Atomic isotopic ratio measurements

Separating stars enriched in the s- and r-processes of nucleosynthesis is usually done by analysing element ratios of ”mainly s-process” elements (like Ba or La) to ”mainly r-process” elements (like Eu). The situation gets more complex when analysing CEMP-rs stars, which are Carbon-Enriched Metal-Poor objects enriched in a mixture of s- and r-elements. These objects, possibly resulting from the i-process of nucleosynthesis, are notoriously difficult to classify based on elemental ratio. Recent theoretical studies have outlined that the s-, i- and r-processes produce distinct isotopic mixtures. However, isotopic abundances are notoriously difficult to measure from atomic lines, because isotopic shifts of atomic lines are negligible compared to the line width. However, in contrast with the spectral lines of even isotopes, the lines of the odd isotopes are affected by hyperfine splitting (HFS). It is thus possible to measure the odd fraction of the isotopic mixture f(Ba,odd) and to relate it to a given nucleosynthetic process (either s-process, or i/r-processes). In this talk, some atomic isotopic diagnostics will be reviewed. Recent progress on how the isotopic mixture can constrain nucleosynthetic processes will be presented. The current limits on f(Ba,odd) determinations from high-resolution spectra will be addressed.