We use observations from the APOGEE survey to explore the relationship between stellar parameters and multiplicity. We combine high-resolution repeat spectroscopy for 41,363 dwarf and subgiant stars with abundance measurements from the APOGEE pipeline and distances and stellar parameters derived using textit{Gaia} DR2 parallaxes from cite{Sanders2018} to identify and characterise stellar multiples with periods below 30 years, corresponding to drvm$gtrsim$ 3 kms, where drvm is the maximum APOGEE-detected shift in the radial velocities. Chemical composition is responsible for most of the variation in the close binary fraction in our sample, with stellar parameters like mass and age playing a secondary role. In addition to the previously identified strong anti-correlation between the close binary fraction and feh, we find that high abundances of $alpha$ elements also suppress multiplicity at most values of feh sampled by APOGEE. The anti-correlation between $alpha$ abundances and multiplicity is substantially steeper than that observed for Fe, suggesting C, O, and Si in the form of dust and ices dominate the opacity of primordial protostellar disks and their propensity for fragmentation via gravitational stability. Near feh{} = 0 dex, the bias-corrected close binary fraction ($a<10$ au) decreases from $approx$ 100 per cent at alh{} = $-$0.2 dex to $approx$ 15 per cent near alh{} = 0.08 dex, with a suggestive turn-up to $approx$20 per cent near alh{} = 0.2. We conclude that the relationship between stellar multiplicity and chemical composition for sun-like dwarf stars in the field of the Milky Way is complex, and that this complexity should be accounted for in future studies of interacting binaries.
Download