The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510

TL;DR

This study analyzes the unique chemical abundance pattern of the extremely metal-poor star RAVE J183013.5-455510, revealing insights into early neutron-capture processes and stellar evolution at low metallicities.

Contribution

It provides the first detailed spectroscopic analysis of this star, suggesting non-standard r-process sources and possible origins from multiple progenitor types.

Findings

Star has [Fe/H] = -3.57, one of the lowest metallicities observed.

Enhanced neutron-capture elements suggest non-standard r-process sources.

Star's orbital properties align with the Galactic metal-weak thick disk.

Abstract

We report on the spectroscopic analysis of RAVE J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [Fe/H]=-3.57, this is one of the lowest metallicity stars currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the Solar System r-process predictions suggest that there must have been a non-standard source of r-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually fast velocities in a neutron star merger event. We also explore the possibility that the neutron-capture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE J1830-4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.