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

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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.


  • R. D. Jeffries
  • R. J. Jackson
  • M. Cottaar
  • S. E. Koposov
  • A. C. Lanzafame
  • M. R. Meyer
  • L. Prisinzano
  • S. Randich
  • G. G. Sacco
  • E. Brugaletta
  • M. Caramazza
  • F. Damiani
  • E. Franciosini
  • A. Frasca
  • G. Gilmore
  • G. Micela
  • E. Alfaro
  • E. Pancino
  • A. Recio-Blanco
  • P. De laverny
  • J. Lewis
  • L. Magrini
  • L. Morbidelli
  • M. T. Costado
  • P. Jofre
  • A. Klutsch
  • K. Lind
  • E. Maiorca
Enheter & grupper

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Astronomi, astrofysik och kosmologi


TidskriftAstronomy & Astrophysics
StatusPublished - 2014
Peer review utfördJa

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