The Gaia DR2 view of the Gamma Velorum cluster: resolving the 6D structure

TL;DR

This study uses Gaia DR2 data to resolve the 6D structure of the Gamma Velorum cluster, revealing two distinct populations with different distances and kinematics, and suggesting they are independent clusters along the same line of sight.

Contribution

The paper provides the first detailed 6D spatial and kinematic analysis of the Gamma Velorum cluster, identifying two separate populations with different distances and motions.

Findings

Gamma Vel A is closer at ~345 pc; Gamma Vel B is farther at ~383 pc.

The two populations are nearly coeval.

Gamma Vel B is expanding.

Abstract

Gaia-ESO Survey observations of the young Gamma Velorum cluster led to the discovery of two kinematically-distinct populations, Gamma Vel A and B, respectively, with population B extended over several square degrees in the Vela OB2 association. Using the Gaia DR2 data for a sample of high-probability cluster members, we find that the two populations differ not only kinematically, but are also located at different distances along the line of sight, with the main cluster Gamma Vel A being closer. A combined fit of the two populations yields $\varpi_A = 2.895 \pm 0.008$ mas and $\varpi_B = 2.608 \pm 0.017$ mas, with intrinsic dispersions of $0.038 \pm 0.011$ mas and $0.091 \pm 0.016$ mas, respectively. This translates into distances of $345.4^{+1.0+12.4}_{-1.0-11.5}\,$ pc and $383.4^{+2.5+15.3}_{-2.5-14.2}\,$ pc, respectively, showing that Gamma Vel A is closer than Gamma Vel B by $\sim$38 pc. We find that the two clusters are nearly coeval, and that Gamma Vel B is expanding. We suggest that Gamma Vel A and B are two independent clusters located along the same line of sight.