We propose a Stellar Locus OuTlier ( SLOT ) method to determine the binary fraction of main-sequence stars statistically .
The method is sensitive to neither the period nor mass-ratio distributions of binaries , and able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes .
We have applied the SLOT method to two samples of stars from the SDSS Stripe 82 , constructed by combining the re-calibrated SDSS photometric data with respectively the spectroscopic information from the SDSS and LAMOST surveys .
For the SDSS spectroscopic sample , we find an average binary fraction for field FGK stars of 41 % \pm 2 % .
The fractions decrease toward late spectral types , and are respectively 44 % \pm 5 % , 43 % \pm 3 % , 35 \% \pm 5 \% , and 28 \% \pm 6 \% for stars of g - i colors between 0.3 – 0.6 , 0.6 – 0.9 , 0.9 – 1.2 , and 1.2 – 1.6 mag .
A modest metallicity dependence is also found .
The fraction decreases with increasing metallicity .
For stars of [ Fe/H ] between -0.5 – 0.0 , -1.0 – -0.5 , -1.5 – -1.0 , and -2.0 – -1.5 dex , the inferred binary fractions are 37 \% \pm 3 \% , 39 \% \pm 3 \% , 50 \% \pm 9 \% , and 53 \% \pm 20 \% , respectively .
We have further divided the sample into stars from the thin disk , the thick disk , the transition zone between them , and the halo .
The results suggest that the Galactic thin and thick disks have comparable binary fractions , whereas the Galactic halo contains a significantly larger fraction of binaries .
Applying the method to the LAMOST spectroscopic sample yields consistent results .
Finally , other potential applications and future work with the method are discussed .