A ring in a shell: the large-scale 6D structure of the Vela OB2 complex

TL;DR

This study uses Gaia DR2 data to analyze the large-scale 6D structure and kinematics of the Vela OB2 association, revealing its composition of small groups, its expansion pattern, and its likely formation triggered by a prior shell expansion.

Contribution

It provides a detailed 6D spatial and kinematic characterization of Vela OB2, linking its formation to the expansion of the IRAS Vela Shell and identifying its substructure.

Findings

Vela OB2 consists of multiple small groups with a total mass over 2330 solar masses.

The stars trace the edge of the IRAS Vela Shell and show signs of expansion.

The shell expansion predates the formation of Vela OB2 and likely triggered star formation.

Abstract

The Vela OB2 association is a group of 10 Myr stars exhibiting a complex spatial and kinematic substructure. The all-sky Gaia DR2 catalogue contains proper motions, parallaxes (a proxy for distance) and photometry that allow us to separate the various components of Vela OB2. We characterise the distribution of the Vela OB2 stars on a large spatial scale, and study its internal kinematics and dynamic history. We make use of Gaia DR2 astrometry and published Gaia-ESO Survey data. We apply an unsupervised classification algorithm to determine groups of stars with common proper motions and parallaxes. We find that the association is made up of a number of small groups, with a total current mass over 2330 Msun. The three-dimensional distribution of these young stars trace the edge of the gas and dust structure known as the IRAS Vela Shell across 180 pc and shows clear signs of expansion. We propose a common history for Vela OB2 and the IRAS Vela Shell. The event that caused the expansion of the shell happened before the Vela OB2 stars formed, imprinted the expansion in the gas the stars formed from, and most likely triggered star formation.