We estimate the fraction of F , G , K stars with close binary companions by analysing multi-epoch stellar spectra from Sloan Digital Sky Survey ( SDSS ) and LAMOST for radial velocity variations .
We employ a Bayesian method to infer the maximum likelihood of the fraction of binary stars with orbital periods of 1000 days or shorter , assuming a simple model distribution for a binary population with circular orbits .
The overall inferred fraction of stars with such a close binary companion is 43.0 \% \pm 2.0 \% for a sample of F , G , K stars from SDSS SEGUE , and 30 \% \pm 8.0 \% in a similar sample from LAMOST .
The apparent close binary fraction decreases with the stellar effective temperature .
We divide the SEGUE and LEGUE data into three subsamples with different metallicity ( \mathrm { [ Fe / H ] } < -1.1 ; -1.1 < \mathrm { [ Fe / H ] } < -0.6 ; -0.6 < \mathrm { [ Fe / H ] } ) , for which the inferred close binary fractions are 56 \pm 5.0 \% , 56.0 \pm 3 \% , and 30 \pm 5.7 \% .
The metal-rich stars from our sample are therefore substantially less likely to possess a close binary companion than otherwise similar stars drawn from metal-poor populations .
The different ages and formation environments of the Milky Way ’ s thin disk , thick disk and halo may contribute to explaining these observations .
Alternatively metallicity may have a significant effect on the formation and/or evolution of binary stars .