Not that simple: the metallicity dependence of the wide binary fraction changes with separation and stellar mass

TL;DR

This study investigates how the wide binary fraction's dependence on metallicity varies with stellar temperature, separation, and disk type, revealing complex relationships that inform binary formation theories.

Contribution

It provides new observational evidence showing the metallicity dependence of the wide binary fraction varies with separation, stellar mass, and disk type, highlighting the complexity of binary formation.

Findings

WBF-metallicity relationship depends on temperature for thin-disk stars.

The relationship changes from negative to positive as temperature increases.

The WBF-metallicity trend varies with separation, showing anti-correlation at small separations and a peak at certain metallicities.

Abstract

The metallicity dependence of the wide binary fraction (WBF) is critical for studying the formation of wide binaries. While controversial results have been found in recent years. Here we combine the wide binary catalog recognized from Gaia EDR3 and stellar parameters from LAMOST to investigate this topic. Taking bias of the stellar temperature at given separations into account, we find that the relationship between the WBF and metallicity depends on temperature for the thin-disk at s > 200 AU. It changes from negative to positive as the temperature increases from 4000 K to 7500 K. This temperature/mass dependence is not seen for the thick-disk. Besides, the general tendency between the WBF and metallicity varies with the separation, consistent with previous results. It shows anti-correlation at small separations, s < 200 AU for the thin-disk and s < 600 AU for the thick-disk. Then it becomes an "arcuate" shape at larger separations (hundreds to thousands of AU), peaking at [Fe/H] ~ 0.1 for the thin-disk and [Fe/H] ~ -0.5 for the thick disk. Finally it becomes roughly flat for the thin-disk at 1000 < s < 10000 AU. Our work provides new observational evidences for theoretical studies on binary formation and evolution.