Mapelli, M.; Vallenari, A.; Jeffries, R. D.; Gavagnin, E.; Cantat-Gaudin, T.; Sacco, G. G.; Meyer, M. R.; Alfaro, E. J.; Costado, M.; Damiani, F.; Frasca, A.; Lanzafame, A. C.; Randich, S.; Sordo, R.; Zaggia, S.; Micela, G.; Flaccomio, E.; Pancino, E.; Bergemann, M.; Hourihane, A.; Lardo, C.; Magrini, L.; Morbidelli, L.; Prisinzano, L.; Worley, C. C.
Astronomy & Astrophysics, Volume 578, id.A35, 11 pp. (2015).
The Gaia-ESO Survey has recently unveiled the complex kinematic signature of the Gamma Velorum cluster: this cluster is composed of two kinematically distinct populations (hereafter, population A and B), showing two different velocity dispersions and a relative ~ 2 km s-1 radial velocity (RV) shift. In this paper, we propose that the two populations of the Gamma Velorum cluster originate from two different sub-clusters, born from the same parent molecular cloud. We investigate this possibility by means of direct-summation N-body simulations. Our scenario is able to reproduce not only the RV shift and the different velocity dispersions, but also the different centroid (~0.5 pc), the different spatial concentration and the different line-of-sight distance (~5 pc) of the two populations. The observed 1-2 Myr age difference between the two populations is also naturally explained by our scenario, in which the two sub-clusters formed in two slightly different star formation episodes. Our simulations suggest that population B is strongly supervirial, while population A is close to virial equilibrium. We discuss the implications of our models for the formation of young star clusters and OB associations in the Milky Way.