Abstract
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
Gaia DR2 parallaxes from Sanders & Das 2018 to identify and characterise
stellar multiples with periods below 30 years, corresponding to
$\Delta$RV$_max\gtrsim$ 3 km s$^-1$, where $\Delta$RV$_max$ 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 Fe/H, we find that high abundances of $\alpha$ elements
also suppress multiplicity at most values of Fe/H 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 Fe/H = 0, the
bias-corrected close binary fraction ($a<10$ au) decreases from $\approx$ 100\%
at $\alpha$/H = $-$0.2 to $\approx$ 15\% near $\alpha$/H = 0.08, with a
suggestive turn-up to $\approx$20\% near $\alpha$/H = 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.
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