G112-43/44: A metal-poor binary star with a unique chemical composition and kinematics like the Helmi streams

TL;DR

This study investigates the chemical composition and kinematics of the metal-poor binary star G112-43/44, revealing its association with the Helmi streams and suggesting supernova enrichment as a possible origin for its peculiar abundances.

Contribution

It provides the first detailed chemical and kinematic analysis of G112-43/44, linking its properties to the Helmi streams and exploring supernova models for its abundance anomalies.

Findings

G112-43/44's abundances are consistent with accreted stars from Gaia-Enceladus.

Enhanced Mn/Fe, Ni/Fe, Cu/Fe, and Zn/Fe suggest supernova enrichment.

Kinematics confirm G112-43/44 belongs to the Helmi streams.

Abstract

G112-43/44, alias BD+00_2058 A and B, is a metal-poor ([Fe/H] = -1.3) wide-orbit binary star with extreme kinematics. We use high-precision determinations of the chemical compositions of 94 metal-poor dwarf stars in the solar neighbourhood to compare abundance ratios for G112-43/44 with ratios for stars having similar metallicity taking into account the effect of deviations from local thermodynamic equilibrium on the derived abundances, and Gaia EDR3 data are used to compare the kinematics. The abundances of the two components of G112-43/44 agree within 0.05 dex for nearly all elements, but there is a hint of a correlation of the difference in [X/H] with elemental condensation temperature, which may be due to planet-star interactions. The Mg/Fe, Si/Fe, Ca/Fe, and Ti/Fe ratios of G112-43/44 agree with the corresponding ratios for accreted (Gaia-Enceladus) stars, but Mn/Fe, Ni/Fe, Cu/Fe, and Zn/Fe are significantly enhanced. The kinematics show that G112-43/44 belongs to the Helmi streams in the solar neighbourhood and in view of this, we discuss if the abundance peculiarities of G112-43/44 can be explained by chemical enrichment from supernovae events in the progenitor dwarf galaxy of the Helmi streams. Interestingly, yields calculated for a helium shell detonation Type Ia supernova model can explain the enhancement of Mn/Fe, Ni/Fe, Cu/Fe, and Zn/Fe in G112-43/44 and three other alpha-poor stars in the Galactic halo, one of which have Helmi streams kinematics. The helium shell detonation model predicts, however, also enhanced abundance ratios of Ca/Fe, Ti/Fe, and Cr/Fe in disagreement with the observed ratios.