Multiplicity among the cool supergiants in the Magellanic Clouds
  The characterisation of the multiplicity of high-mass stars is of fundamental
importance to understand their evolution, the diversity of observed
core-collapse supernovae and the formation of gravitational wave progenitor
systems. Despite that, until recently, one of the final phases of massive star
evolution -- the cool supergiant phase -- has received comparatively little
attention. In this study we aim to explore the multiplicity among the cool
supergiants (CSGs) in the Large and Small Magellanic Clouds (LMC and SMC,
respectively). To do this we compile extensive archival radial velocity (RV)
measurements for over 1000 CSGs from the LMC and SMC, spanning a baseline of
over 40 years. By statistically correcting the RV measurements of each stellar
catalogue to the Gaia DR2 reference frame we are able to effectively compare
these diverse observations. We identify 45 CSGs where RV variations cannot be
explained through intrinsic variability, and are hence considered binary
systems. We obtain a minimum binary fraction of $15\pm4\%$ for the SMC and of
$14\pm5\%$ for the LMC. Combining these results, we determine a minimum binary
fraction of $15\pm3\%$ for CSGs. These results are in good agreement with
previous results which apply a correction to account for observational biases.
These results add strength to the hypothesis that the binary fraction of CSGs
is significantly lower than their main-sequence counterparts. Going forward, we
stress the need for long-baseline multi-epoch spectroscopic surveys to cover
the full parameter space of CSG binary systems.
