The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

TY - JOUR

T1 - The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

AU - Jeffries, R. D.

AU - Jackson, R. J.

AU - Cottaar, M.

AU - Koposov, S. E.

AU - Lanzafame, A. C.

AU - Meyer, M. R.

AU - Prisinzano, L.

AU - Randich, S.

AU - Sacco, G. G.

AU - Brugaletta, E.

AU - Caramazza, M.

AU - Damiani, F.

AU - Franciosini, E.

AU - Frasca, A.

AU - Gilmore, G.

AU - Feltzing, Sofia

AU - Micela, G.

AU - Alfaro, E.

AU - Bensby, Thomas

AU - Pancino, E.

AU - Recio-Blanco, A.

AU - De laverny, P.

AU - Lewis, J.

AU - Magrini, L.

AU - Morbidelli, L.

AU - Costado, M. T.

AU - Jofre, P.

AU - Klutsch, A.

AU - Lind, K.

AU - Maiorca, E.

PY - 2014

Y1 - 2014

N2 - 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. We 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 6708 angstrom 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 +/- 0.16 km s(-1), consistent with virial equilibrium. The second has a broader dispersion of 1.60 +/- 0.37 km s(-1) and is offset from the first by congruent to 2 kms(-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 (>= 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.

AB - 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. We 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 6708 angstrom 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 +/- 0.16 km s(-1), consistent with virial equilibrium. The second has a broader dispersion of 1.60 +/- 0.37 km s(-1) and is offset from the first by congruent to 2 kms(-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 (>= 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.

KW - stars: pre-main sequence

KW - stars: kinematics and dynamics

KW - open clusters

KW - and associations: individual: gamma2 Velorum

KW - stars: formation

U2 - 10.1051/0004-6361/201323288

DO - 10.1051/0004-6361/201323288

M3 - Article

VL - 563

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 1432-0746

M1 - A94

ER -