Lithium abundance in a turnoff halo star on an extreme orbit

TL;DR

This study analyzes the lithium abundance in a high-velocity, extreme halo star, confirming that the lithium plateau's low scatter persists regardless of stellar kinematics, and compares it with typical old turnoff stars.

Contribution

It provides the first detailed abundance analysis of an extreme halo star on a retrograde orbit, supporting the universality of the lithium plateau.

Findings

Lithium abundance in the star aligns with the plateau in old, metal-poor stars.

The star's abundance ratios are typical of old turnoff stars.

The lithium plateau's low scatter is independent of stellar kinematic properties.

Abstract

The lithium abundance in turnoff stars of the old population of our Galaxy is remarkably constant in the metallicity interval -2.8\textless{}[Fe/H] \textless{}-2.0, defining a plateau. The Li abundance of these turnoff stars is clearly lower than the abundance predicted by the primordial nucleosynthesis in the frame of the standard Big Bang nucleosynthesis. Different scenarios have been proposed for explaining this discrepancy, along with the very low scatter of the lithium abundance around the plateau. The recently identified very high velocity star, WISE J072543.88-235119.7 appears to belong to the old Galactic population, and appears to be an extreme halo star on a bound, retrograde Galactic orbit. In this paper, we study the abundance ratios and, in particular the lithium abundance, in this star. The available spectra (ESO-Very Large Telescope) are analyzed and the abundances of Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba are determined.The abundance ratios in WISE J072543.88-235119.7 are those typical of old turnoff stars. The lithium abundance in this star ~is in close agreement with the lithium abundance found in the metal-poor turnoff stars located at moderate distance from the Sun. This high velocity star confirms, in an extreme case, that the very small scatter of the lithium plateau persists independent of the dynamic and kinematic properties of the stars.