Abstract
Metal-poor stars with measurable r-process element abundances provide key clues to the production site(s) of the r-process and how its products are mixed with the surrounding medium. While the number of stars exhibiting strong enhancements of r-process elements has grown over the years, the lower “floor” of r-process enrichment in metal-poor stars has yet to be established, largely in part due to the difficulty in detecting weak neutron-capture element absorption lines in stellar spectra. Here we present detailed abundances of 16 neutron-capture elements for a star exhibiting the lowest level of r-process enrichment yet detected and still following the solar system r-process pattern. Taken into consideration with most of the r- process enriched stars currently in the literature, the range of r-process element enrichment spanned by this sample is at least ∼1.3dex or a factor of more than 20. That the r-process abundance pattern is unchanged while the degree of enrichment varies may suggest that the r- process yields are constant while the gas mass into which they are mixed varies. Given that all stars have similar [Fe/H] values then suggests that only one or few previous stellar generations provided the observed chemical abundances, meaning that perhaps only one r-process event occurred prior to their formation. This would be consistent with a (near) constant r-process yield per event. Obtaining detailed element abundances for stars with mild r-process element enhancements is necessary to better constrain the ubiquity of the r-process pattern, the yields of r-process elements, and the site of its production.
Highlights
Understanding r-process nucleosynthesis is a central topic of nuclear physics theory and experiments
Much has to still be learned about it, including its astrophysical site and whether it is universal across the full range of neutron-capture elements or just for the heaviest elements
Only stars with large overabundances have been analyzed in detail since they have proved to be the most promising stars to study the details of the stellar r-process pattern [2]. This led to the remarkable discovery that the r-process element abundance pattern appears to be universal, as the scaled solar r-process pattern matches that of these metal-poor stars nearly perfectly [3, 4, 5]
Summary
Understanding r-process nucleosynthesis is a central topic of nuclear physics theory and experiments. Comparison with the scaled solar r-process pattern revealed this star to show signs of r-process nucleosynthesis, i.e. HE 0147−4606 formed from a gas cloud that was enriched by an r-process event, at a very modest level.
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