Multiple kinematical populations in Vela OB2 from Gaia DR1 data
F. Damiani1, L. Prisinzano1, R. D. Jeffries2, G. G. Sacco3, S. Randich3 and G. Micela1
<<The Vela OB2 association spans a wide sky region inside the Gum nebula (Pettersson 2008) and has been subject to an increasing number of studies in recent years..., as we describe below, the Gaia proper-motion data show clear evidence of a double population in Vela OB2, with intriguing analogies with those from the Gaia-ESO survey data.
Using their well-defined mean proper motions, we may trace back in time the apparent average positions of populations C and D over a few Myr.The arrows in Fig. 4
show the positions of γ2 Vel
and NGC 2547
extrapolated back 1.1 Myr, using the(error-weighted) mean proper motions of concentrated populations C and D.This shows that their (sky-projected) distance is now slowly increasing,while it reached a minimum value of 0.65 degrees (4.04 pc) 1.1 Myr ago. This is a small enough value, compared to the apparent sizes of both γ2
Vel and NGC 2547 clusters, to expect a significant dynamical interaction between them, provided that also their distances from the Sun are (or were at that time) coincident within a few pc. An intriguing possibility is therefore that population B in the γ2
Vel cluster originates from a tidal stripping event during a close encounter with the (denser) cluster NGC 2547. One difficulty with this hypothesis lies in the offset of the RV distribution of population B with respect to that of population A, whereas tidal stripping may be expected to create two symmetric (leading and trailing) tails.
To summarise, the Gaia DR1 data indicate that populations C and D had the highest probability of a mutual interaction in the past 1−1.5 Myr. Determining if this has actually taken place depends on a more accurate determination of the populations’ respective parallaxes, which are expected from future Gaia data releases. Future Gaia data releases will permit a more accurate determination of its properties.