期刊
ASTRONOMY & ASTROPHYSICS
卷 563, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201323288
关键词
stars: pre-main sequence; stars: kinematics and dynamics; open clusters and associations: individual: gamma2 Velorum; stars: formation
资金
- ESO Telescopes at the La Silla Paranal Observatory [188.B-3002]
- ESF (European Science Foundation) through the GREAT (Gaia Research for European Astronomy Training) Research Network Program [3855, 4127, 4415]
- Gaia Research for European Astronomy Training (GREAT-ITN) Marie Curie network
- European Union Seventh Framework Programme [FP7] [264895]
- European Union FP7 programme through ERC [320360]
- Leverhulme Trust [RPG-2012-541]
- INAF
- Ministero dell' Istruzione, dell' Universita e della Ricerca (MIUR) in the form of the grant Premiale VLT
- UK Science and Technology Facilities Council
- STFC [ST/J000035/1, ST/L001381/1, ST/G002355/1, ST/J001384/1, PP/D000955/1, PP/F000057/1, ST/J00541X/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/L001381/1, ST/G002355/1, ST/J000035/1, PP/D000955/1, ST/H00243X/1, ST/J001384/1, PP/F000057/1, ST/J00541X/1] Funding Source: researchfish
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.
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