Expanding associations in the Vela-Puppis region: 3D structure and kinematics of the young population

TL;DR

This study uses Gaia DR2 data to analyze the 3D structure and kinematics of young stars in the Vela-Puppis region, revealing multiple expanding groups with varied ages and anisotropic expansion patterns, suggesting complex star formation history.

Contribution

It introduces an unsupervised classification approach to identify and characterize multiple young stellar groups in Vela-Puppis using Gaia data, highlighting their expansion and age substructure.

Findings

Seven main stellar groups with different ages identified.

All groups exhibit expansion, mostly anisotropic.

Star formation likely occurred over a prolonged period in a turbulent cloud.

Abstract

The Vela-Puppis region is known to host the Vela OB2 association as well as several young clusters featuring OB and pre-main sequence stars. Several spatial and kinematic subgroups have been identified in the recent years. By grouping stars based on their positions and velocity we can address the quetion of the dynamical history of the region and the mechanisms that drove stellar formation. The Gaia DR2 astrometry and photometry enables us to characterise the 3D spatial and 3D kinematic distribution of young stars and to estimate the ages of the identified components. We use an unsupervised classification method to group stars based on their proper motions and parallax. We perform a study of the expansion rates of the different identified groups from 3D velocities, and from corrected tangential velocities. We make use of theoretical isochrones to estimate ages. The young stars can be separated into seven main groups of different ages and kinematical distribution. All groups are found to be expanding, although the expansion is mostly not isotropic. The size of the region, the age substructure, and the anistropic expansion rates are compatible with a prolonged period of star formation in a turbulent molecular cloud, and that the dispersion of the stars cannot be explained by gas expulsion alone.