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

Abstract

The nearby (distance ~ 350-400 pc), rich Vela OB2 association, includes γ<SUP>2</SUP> 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 surrounding γ<SUP>2</SUP> Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35 Myr cluster located two degrees south of γ<SUP>2</SUP> 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 around γ<SUP>2</SUP> Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degrees in the Vela OB2 association. This population could have originally been part of a cluster around γ<SUP>2</SUP> Velorum that expanded after gas expulsion or formed in a less dense environment that is spread over the whole Vela OB2 region. <P />Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).Table 1 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/L7">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/L7</A>