Mon. Not. R. Astron. Soc., 393, 538-556 (2009/February-3)
The stellar association around gamma Velorum and its relationship with Vela OB2.
JEFFRIES R.D., NAYLOR T., WALTER F.M., POZZO M.P. and DEVEY C.R.
Abstract (from CDS):
We present the results of a photometric BVI survey of 0.9deg2 around the Wolf-Rayet binary γ2 Vel and its early-type common proper motion companion γ1 Vel (together referred to as the γ Vel system). Several hundred pre-main-sequence (PMS) stars are identified and the youth of a subset of these is spectroscopically confirmed by the presence of lithium in their atmospheres, Hα emission and high levels of X-ray activity. We show that the PMS stars are kinematically coherent and spatially concentrated around γ Vel. The PMS stars have similar proper motions to γ Vel, to main-sequence (MS) stars around γ Vel and to early-type stars of the wider Vela OB2 association of which γ2 Vel is the brightest member. The ratio of MS stars to low-mass (0.1-0.6M☉) PMS stars is consistent with a Kroupa mass function. MS fitting to stars around γ Vel gives an association distance modulus of 7.76±0.07mag, which is consistent with a similarly determined distance for Vela OB2 and also with interferometric distances to γ2 Vel. High-mass stellar models indicate an age of 3-4Myr for γ2 Vel, but the low-mass PMS stars have ages of ≃10Myr according to low-mass evolutionary models and 5-10Myr by empirically placing them in an age sequence with other clusters based on colour-magnitude diagrams and lithium depletion. We conclude that the low-mass PMS stars form a genuine association with γ Vel, and this is a subcluster within the larger Vela OB2 association. We speculate that γ2 Vel formed after the bulk of the low-mass stars, expelling gas, terminating star formation and unbinding the association. The velocity dispersion of the PMS stars is too low for this star-forming event to have produced all the stars in the extended Vela OB2 association. Instead, star formation must have been initiated at several sites within a molecular cloud either sequentially or simultaneously after some triggering event.
© 2009 The Authors. Journal compilation © 2009 RAS
stars: formation - stars: pre-main-sequence - stars: Wolf-Rayet - open clusters and associations: individual: Vela OB2
VizieR on-line data:
<Available at CDS (J/MNRAS/393/538): table2.dat table3.dat table4a.dat table4b.dat>
Table 2: [JNW2009] FF NNNN N=86972.
The Stellar association around gamma Velorum = Name Gam Vel Subcluster.
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