Research Note

Lithium abundance in a turnoff halo star on an extreme orbit^⋆,⋆⋆

GEPI, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, Observatoire Place Jules Janssen, 92195 Meudon, France
e-mail: monique.spite@obspm.fr

Received: 2 July 2015
Accepted: 29 August 2015

Abstract

Context. The lithium abundance in turnoff stars of the old population of our Galaxy is remarkably constant in the metallicity interval −2.8 < [Fe/H] < −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.

Aims. The recently identified very high velocity star, WISE J0725–2351 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.

Methods. 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.

Results. The abundance ratios in WISE J0725–2351 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.