The kinematics of young stellar population in the W5 region of the Cassiopeia OB6 association: implication on the formation process of stellar associations

TL;DR

This study investigates the kinematics and spatial distribution of young stars in the W5 region, revealing multiple star formation events and substructures shaped by feedback and dynamical processes within a giant molecular cloud.

Contribution

It provides a detailed kinematic analysis of young stellar groups in W5 using Gaia and radial velocity data, highlighting multiple star formation episodes and their implications.

Findings

W5 contains eight stellar groups with distinct ages and structures.

Three dense groups show expansion patterns and similar ages (~5 Myr).

Southern groups suggest formation via dynamical ejection or multiple events.

Abstract

The star-forming region W5 is a major part of the Cassiopeia OB6 association. Its internal structure and kinematics may provide hints of the star formation process in this region. Here, we present a kinematic study of young stars in W5 using the Gaia data and our radial velocity data. A total 490 out of 2,000 young stars are confirmed as members. Their spatial distribution shows that W5 is highly substructured. We identify a total of eight groups using the k-means clustering algorithm. There are three dense groups in the cavities of H II bubbles, and the other five sparse groups are distributed at the ridge of the bubbles. The three dense groups have almost the same ages (5 Myr) and show a pattern of expansion. The scale of their expansion is not large enough to account for the overall structure of W5. The three northern groups are, in fact, 3 Myr younger than the dense groups, which indicates the independent star formation events. Only one group of them shows the signature of feedback-driven star formation as its members move away from the eastern dense group. The other two groups might have formed in a spontaneous way. On the other hand, the properties of two southern groups are not understood as those of a coeval population. Their origins can be explained by dynamical ejection of stars and multiple star formation. Our results suggest that the substructures in W5 formed through multiple star-forming events in a giant molecular cloud.