The GALAH survey: Multiple stars and our Galaxy. I. A comprehensive
  method for deriving properties of FGK binary stars
  Binary stellar systems form a large fraction of the Galaxy's stars. They are
useful as laboratories for studying the physical processes taking place within
stars, and must be correctly taken into account when observations of stars are
used to study the structure and evolution of the Galaxy. We present a sample of
12760 well-characterised double-lined spectroscopic binaries that are
appropriate for statistical studies of the binary populations. They were
detected as SB2s using a t-distributed stochastic neighbour embedding (t-SNE)
classification and a cross-correlation analysis of GALAH spectra. This sample
consists mostly of dwarfs, with a significant fraction of evolved stars and
several dozen members of the giant branch. To compute parameters of the primary
and secondary star ($T_{\rm eff[1,2]}$, $\log g_{[1,2]}$, [Fe/H], $V_{r[1,2]}$,
$v_{\rm mic[1,2]}$, $v_{\rm broad[1,2]}$, $R_{[1,2]}$, and $E(B-V)$), we used a
Bayesian approach that includes a parallax prior from Gaia DR2, spectra from
GALAH, and apparent magnitudes from APASS, Gaia DR2, 2MASS, and WISE. The
derived stellar properties and their distributions show trends that are
expected for a population of close binaries (a $<$ 10 AU) with mass ratios $0.5
\leq q \leq 1$. The derived metallicity of these binary stars is statistically
lower than that of single dwarf stars from the same magnitude-limited sample.
