# The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo

## TL;DR

This paper reports the discovery of a metal-poor star in the Milky Way halo with unique low-alpha and r-process-enhanced chemical signatures, likely originating from an accreted dwarf galaxy with a complex enrichment history.

## Contribution

It identifies a new r-process-enhanced, low-alpha metal-poor star and analyzes its chemical and kinematic properties, revealing insights into its origin and enrichment processes.

## Key findings

- Star has [Fe/H] = -1.86 and is likely a horizontal branch star.
- Star shows subsolar [X/Fe] ratios for light, alpha, and Fe-peak elements.
- Kinematics suggest it was accreted from a dwarf galaxy with r-process enrichment.

## Abstract

A new moderately r-process-enhanced metal-poor star, RAVE J093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937-0626 is likely a horizontal branch star. At [Fe/H] = -1.86, J0937-0626 is found to have subsolar [X/Fe] ratios for nearly every light, alpha, and Fe-peak element. The low [alpha/Fe] ratios can be explained by an ~0.6 dex excess of Fe; J0937-0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H] = -2.5 suggests that J0937-0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937-0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937-0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937-0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.