Search for Stellar Flybys in the Sco-Cen OB Association with the Gaia DR2

TL;DR

This study uses Gaia DR2 data to trace stellar flybys in the Sco-Cen OB Association, aiming to empirically assess their influence on debris disk morphology and identify past close encounters.

Contribution

It provides the first empirical analysis of stellar flybys in Sco-Cen, identifying 119 stars with past flybys and examining their potential impact on circumstellar disks.

Findings

119 stars experienced flybys within one Hill radius

No significant correlation between flybys and infrared excess

Some stars with flybys host symmetric circumstellar disks

Abstract

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.