Kavli Affiliate: Anna Frebel
| First 5 Authors: Avrajit Bandyopadhyay, Rana Ezzeddine, Carlos Allende Prieto, Nima Aria, Shivani P. Shah
| Summary:
Understanding the abundance pattern of metal-poor stars and the production of
heavy elements through various nucleosynthesis processes offers crucial
insights into the chemical evolution of the Milky Way, revealing primary sites
and major sources of rapid neutron-capture process ($r$-process) material in
the Universe. In this fifth data release from the $R$-Process Alliance, we
present the detailed chemical abundances of 41 faint (down to V = 15.8) and
extremely metal-poor (down to [Fe/H] = -3.3) halo stars selected from the
R-Process Alliance (RPA). We obtained high-resolution spectra for these objects
with the HORuS spectrograph on the Gran Telescopio Canarias. We measure the
abundances of light, alpha, Fe-peak, and neutron-capture elements. We report
the discovery of five CEMP, one limited-$r$, three $r$-I, and four $r$-II
stars, and six Mg-poor stars. We also identify one star of a possible globular
cluster origin at an extremely low metallicity at [Fe/H] = -3.0. This adds to
the growing evidence of a lower limit metallicity floor for globular cluster
abundances. We use the abundances of Fe-peak elements and the alpha-elements to
investigate the contributions from different nucleosynthesis channels in the
progenitor supernovae. We find the distribution of [Mg/Eu] as a function of
[Fe/H] to have different enrichment levels, indicating different possible
pathways and sites of their production. We also reveal differences in the
trends of the neutron-capture element abundances of Sr, Ba, and Eu of various
$r$-I and $r$-II stars from the RPA data releases, which provide constraints on
their nucleosynthesis sites and subsequent evolution.
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