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The structure and 3D kinematics of vela OB2

Armstrong, Joseph J; Wright, Nicholas J; Jeffries, Robin D; Jackson, Richard J; Cantat-Gaudin, Tristan

The structure and 3D kinematics of vela OB2 Thumbnail


Joseph J Armstrong

Richard J Jackson

Tristan Cantat-Gaudin


The kinematics of stars in OB associations can provide insights into their formation, dynamical evolution, and eventual fate. The low-mass stellar content of OB associations are sufficiently numerous as to provide a detailed sampling of their kinematic properties, however spectroscopy is required to confirm the youth of individual stars and to get 3D kinematics. In this paper, we present and analyse results from a large spectroscopic survey of Vela OB2 conducted using 2dF/HERMES on the AAT. This spectroscopy is used to confirm the youth of candidate young stars and determine radial velocities, which are combined with proper motions and parallaxes from Gaia to measure 3D positions and velocities. We identify multiple separate kinematic groups in the region, for which we measure velocity dispersions and infer their virial states. We measure expansion rates for all these groups and find strong evidence for anisotropic expansion in the Vela OB2 association of at least 11s significance in all three dimensions, as well as some evidence for expansion in the ? Vel and P Puppis clusters. We trace back the motions of these groups into the past and find that the open cluster NGC 2547 is an interloper in the Vela OB2 region and actually formed >100 pc away from the association. We conclude that Vela OB2 must have formed with considerable spatial and kinematic substructure over a time-scale of ~10?Myr, with clear temporal substructure within the association, but no clear evidence for an age gradient.

Journal Article Type Article
Acceptance Date Oct 24, 2022
Publication Date Nov 10, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 517
Issue 4
Pages 5704 - 5720
Keywords techniques: spectroscopic; surveys; stars: kinematics and dynamics; stars: pre-main-sequence; open clusters and associations: individual: Vela OB2, NGC 2547, gamma, Vel, P Puppis
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