Large-scale expansion of OB stars in Cygnus

TL;DR

This study uses 3D traceback analysis of OB stars in Cygnus to determine their expansion history, concluding that their large-scale expansion is consistent with turbulence in the primordial molecular cloud rather than feedback from massive stars.

Contribution

It provides the first detailed 3D kinematic analysis of OB stars in Cygnus, demonstrating that their expansion is likely driven by turbulence rather than stellar feedback.

Findings

Stars and clusters were more compact in the past.

Expansion occurred approximately 8 million years ago.

Turbulence, not feedback, explains the expansion patterns.

Abstract

The proper motions (PMs) of OB stars in Cygnus have recently been found to exhibit two large-scale kinematic patterns suggestive of expansion. We perform a 3D traceback on these OB stars, the newly-identified OB associations and related open clusters in the region. We find that there are two groups of stars, associations and clusters and that they were each more compact in the past, reaching their closest approach $7.9^{+3.0}_{-1.8}$ and $8.5^{+0.8}_{-2.8}$ Myr ago. We consider two main scenarios for the driver of these large-scale expansion patterns: feedback-driven expansion from a previous generation of massive stars, and expansion as a result of the turbulent velocity field in the primordial molecular cloud. While it is tempting to attribute such large-scale expansion patterns to feedback processes, we find that the observed kinematics are fully consistent with the turbulent origin, and therefore that the injection of further energy or momentum from feedback is not required. Similar conclusions may be drawn for other star forming regions with large-scale expansion patterns.