Search for Stellar Flybys in the Sco-Cen OB Association with the Gaia
  DR2
  High-contrast imaging studies of debris disks have revealed a significant
diversity in their morphologies, including large-scale asymmetries. Theories
involving stellar flybys, an external source of gravitational disturbance, have
offered a plausible explanation for the origin of these morphological
variations. Our study is an experiment to gain empirical evidence that has been
lacking from such theories. We explore this paradigm by using astrometric and
radial velocity measurements from the Gaia DR2 and ground-based observations to
trace the trajectories of 625 stars in the Sco-Cen OB Association from 5 Myr in
the past to 2 Myr in the future. We identified 119 stars that had at least one
past flyby event occurring within one Hill radius, and 23 of these experienced
flybys within 0.5 Hill radius. We found no evidence of a significant
correlation between the presence of flyby events and infrared excess
detections, although the sample is not uniformly sensitive to infrared excess
emission. Ten stars that had past flyby events host resolved circumstellar
disks that appear relatively symmetric in the existing data except for the
circumbinary disk surrounding HD 106906. We determined the trajectory and
relative velocity of each of these flyby events, and compared these to the
geometry of the spatially-resolved disks. Future work is needed to measure the
kinematics of lower mass stars and to improve sensitivity to circumstellar
disks for the entire sample.
