Binary Star Fractions from the LAMOST DR4

Abstract

Stellar systems composed of single, double, triple or higher-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 multiepoch observations, we analyze the binary fraction of dwarf stars observed with 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-eff and decreases with [Fe/H]. We first investigate the relation between alpha-elements and binary fraction in such a large sample as provided by LAMOST. The old stars with high [alpha/Le] dominate with a higher binary fraction than young stars with low [alpha/Fe]. At the same mass, earlier forming stars possess a higher binary fraction than newly forming ones, which may be related with evolution of the Galaxy.