The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks

TL;DR

This study provides new observational benchmarks for elements between the first and second r-process peaks in metal-poor stars, revealing a possible universality in their abundance patterns and challenging previous assumptions.

Contribution

It offers the first empirical abundance ratios for elements between the first and second r-process peaks, suggesting a common nucleosynthesis source and potential universality among certain light and heavy r-process elements.

Findings

Small star-to-star abundance dispersion (<= 0.13 dex) among several light r-process elements.

Te abundances correlate more closely with lighter r-process elements than heavier ones.

Evidence supporting r-process universality among some elements at and between the first and second peaks.

Abstract

We present new observational benchmarks of rapid neutron-capture process (r-process) nucleosynthesis for elements at and between the first (A ~ 80) and second (A ~ 130) peaks. Our analysis is based on archival ultraviolet and optical spectroscopy of eight metal-poor stars with Se (Z = 34) or Te (Z = 52) detections, whose r-process enhancement varies by more than a factor of 30 (-0.22 <= [Eu/Fe] <= +1.32). We calculate ratios among the abundances of Se, Sr through Mo (38 <= Z <= 42), and Te. These benchmarks may offer a new empirical alternative to the predicted solar system r-process residual pattern. The Te abundances in these stars correlate more closely with the lighter r-process elements than the heavier ones, contradicting and superseding previous findings. The small star-to-star dispersion among the abundances of Se, Sr, Y, Zr, Nb, Mo, and Te (<= 0.13 dex, or 26%) matches that observed among the abundances of the lanthanides and third r-process-peak elements. The concept of r-process universality that is recognized among the lanthanide and third-peak elements in r-process-enhanced stars may also apply to Se, Sr, Y, Zr, Nb, Mo, and Te, provided the overall abundances of the lighter r-process elements are scaled independently of the heavier ones. The abundance behavior of the elements Ru through Sn (44 <= Z <= 50) requires further study. Our results suggest that at least one relatively common source in the early Universe produced a consistent abundance pattern among some elements spanning the first and second r-process peaks.