Binary Star Fractions from the LAMOST DR4

TL;DR

This study estimates the binary star fraction in the Milky Way using LAMOST data, revealing dependencies on stellar temperature, metallicity, and chemical composition, and compares different orbital period models.

Contribution

It introduces a comprehensive analysis of binary fractions using multi-epoch LAMOST data, considering various orbital period distributions and chemical properties.

Findings

Binary fraction increases with stellar temperature.

Binary fraction decreases with metallicity.

Older, alpha-enhanced stars have higher binary fractions.

Abstract

Stellar systems composed of single, double, triple or high-order systems are rightfully regarded as the fundamental building blocks of the Milky Way. Binary stars play an important role in formation and evolution of the Galaxy. Through comparing the radial velocity variations from multi-epoch observations, we analyze the binary fraction of dwarf stars observed with the LAMOST. Effects of different model assumptions such as orbital period distributions on the estimate of binary fractions, are investigated. The results based on log-normal distribution of orbital periods reproduce the previous complete analyses better than the power-law distribution. We find that the binary fraction increases with $T_{\rm eff}$ and decreases with [Fe/H]. We first investigate the relation between $\alpha$-elements and binary fraction in such a large sample as the LAMOST. The old stars with high [$\alpha$/Fe] dominate higher binary fraction than young stars with low [$\alpha$/Fe]. At the same mass, former forming stars possess a higher binary fraction than newly forming ones, which may be related with the evolution of the Galaxy.