Chemical abundances in a high velocity RR Lyrae star near the bulge

TL;DR

This study presents the first chemical abundance analysis of a high-velocity RR Lyrae star near the Galactic bulge, providing insights into its possible origin and the dynamics of low-mass, high-velocity stars in the Milky Way.

Contribution

It offers the first detailed chemical analysis of a low-mass, high-velocity RR Lyrae star, exploring its origin through combined chemical and kinematic data.

Findings

Star has [Fe/H] = -0.9 dex, indicating moderate metallicity.

Chemical tagging does not conclusively determine origin, but suggests possible halo or bulge association.

Star's retrograde orbit and abundances imply acceleration from the halo or interactions with the Milky Way.

Abstract

Low-mass, variable, high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high- or hyper-velocity stars were young stars thought to originate from the Galactic centre. Wide-area surveys like APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities larger than 350 km/s. In this study we present the first abundance analysis of a low-mass, RR Lyrae star, located close to the Galactic bulge, with a space motion of ~ -400 km/s. Using medium-resolution spectra, we derive abundances (including upper limits) of 11 elements. These allow us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] =-0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, combining its retrograde orbit and the derived abundances suggests that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star could be stripped from a star cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.