Context : A key science goal of the Gaia-ESO survey ( GES ) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound .
The clustering of low-mass stars around the massive Wolf-Rayet binary system \gamma ^ { 2 } Velorum was one of the first GES targets .

Aims : To empirically determine the radial velocity precision of GES data , construct a kinematically unbiased sample of cluster members and characterise their dynamical state .

Methods : Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy was used to derive radial velocities and assess membership from the strength of the Li i 6708Å line .
The radial velocity distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries .

Results : The GES radial velocity precision is about 0.25 km s ^ { -1 } and sufficient to resolve velocity structure in the low-mass population around \gamma ^ { 2 } Vel .
The structure is well fitted by two kinematic components with roughly equal numbers of stars ; the first has an intrinsic dispersion of 0.34 \pm 0.16 km s ^ { -1 } , consistent with virial equilibrium .
The second has a broader dispersion of 1.60 \pm 0.37 km s ^ { -1 } and is offset from the first by \simeq 2 km s ^ { -1 } .
The first population is older by 1–2 Myr based on a greater level of Li depletion seen among its M-type stars and is probably more centrally concentrated around \gamma ^ { 2 } Vel .

Conclusions : We consider several formation scenarios , concluding that the two kinematic components are a bound remnant of the original , denser cluster that formed \gamma ^ { 2 } Vel , and a dispersed population from the wider Vela OB2 association , of which \gamma ^ { 2 } Vel is the most massive member .
The apparent youth of \gamma ^ { 2 } Vel compared to the older ( \geq 10 Myr ) low-mass population surrounding it suggests a scenario in which the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars .