The Gaia-ESO survey: Discovery of a spatially extended low-mass population in the Vela OB2 association

The nearby (distance∼350-400 pc), rich Vela OB2 association, includesγ 2 Velorum, one of the most massive binaries in the solar neighbourhood and an excellent laboratory for investigating the formation and early evolution of young clusters. Recent Gaia-ESO survey observations have led to the discovery of two kinematically distinct populations in the young (10-15 Myr) cluster immediately surroundingγ 2 Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35 Myr cluster located two degrees south ofγ 2 Velorum. The radial velocity distribution of lithium-rich pre-main sequence stars shows a secondary population that is kinematically distinct from and younger than NGC 2547. The radial velocities, lithium absorption lines, and the positions in a colour-magnitude diagram of this secondary population are consistent with those of one of the components discovered aroundγ 2 Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degree s in the Vela OB2 association. This population could have originally been part of a cluster aroundγ 2 Velorum that expanded after gas expulsion or formed in a less dense environment that is spread over the whole Vela OB2 region.