Identical or fraternal twins? : The chemical homogeneity of wide binaries from Gaia DR2

TL;DR

This study investigates the chemical homogeneity of wide binary star systems using Gaia DR2 data and high-resolution spectra, finding most pairs are chemically similar, supporting the feasibility of chemical tagging in Galactic archaeology.

Contribution

It provides detailed chemical abundance analysis of 25 wide binary systems, demonstrating their general chemical homogeneity and implications for chemical tagging.

Findings

80% of wide binaries are homogeneous in [Fe/H] below 0.02 dex

Wide binaries are more chemically similar than random star pairs

Some wide binaries show elemental differences up to 0.10 dex

Abstract

One of the high-level goals of Galactic archaeology is chemical tagging of stars across the Milky Way to piece together its assembly history. For this to work, stars born together must be uniquely chemically homogeneous. Wide binary systems are an important laboratory to test this underlying assumption. Here we present the detailed chemical abundance patterns of 50 stars across 25 wide binary systems comprised of main-sequence stars of similar spectral type identified in Gaia DR2 with the aim of quantifying their level of chemical homogeneity. Using high-resolution spectra obtained with McDonald Observatory, we derive stellar atmospheric parameters and precise detailed chemical abundances for light/odd-Z (Li, C, Na, Al, Sc, V, Cu), $\alpha$ (Mg, Si, Ca), Fe-peak (Ti, Cr, Mn, Fe, Co, Ni, Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, Eu) elements. Results indicate that 80% (20 pairs) of the systems are homogeneous in [Fe/H] at levels below 0.02 dex. These systems are also chemically homogeneous in all elemental abundances studied, with offsets and dispersions consistent with measurement uncertainties. We also find that wide binary systems are far more chemically homogeneous than random pairings of field stars of similar spectral type. These results indicate that wide binary systems tend to be chemically homogeneous but in some cases they can differ in their detailed elemental abundances at a level of [X/H] ~ 0.10 dex, overall implying chemical tagging in broad strokes can work.