2002ApJ...575L..75O

The β Pictoris moving group (BPMG) as proposed by Zuckerman et al. is a group of 19 low-mass star systems containing β Pictoris and its protoplanetary disk. This nearest moving group is at a mean distance of 36 pc from the Earth, and these authors have proposed, by means of an H-R diagram, an evolutionary age of 12⁺⁸_–4 Myr for this group. Here, by retracing the three-dimensional orbits of all the members of the BPMG and using a realistic Galactic potential, we find that a first maximum concentration of orbits occurs at 11.5 Myr and in a space region having a maximum size of 24 pc, 3 times smaller than its present size. We consider this region to be the birthplace of the BPMG. This interesting similarity of independently obtained evolutionary and kinematical ages indicates that this group could have already been formed as an unbound system, as observed today. The birthplace of the BPMG is located in a three-dimensional space, at ∼45 pc from the region where the Lower Centaurus Crux (LCC) and Upper Centaurus Lupus (UCL) subgroups of the Scorpius-Centaurus OB association were when they were between 4 and 6 Myr old. At that age, both subgroups were able to produce supernovae (SNe) capable of triggering the formation of the BPMG. This interaction distance could even be smaller, up to ∼26 pc, if SNe exploded in the outer regions of the LCC or UCL near the proposed birthplace of the BPMG. This scenario confirms, at least for the BPMG, the suggestion made by Mamajek & Feigelson and other authors that young unbound nearby stellar associations with ages around ∼10 Myr originated in this OB complex. In contrast to the BPMG, for which we propose a coeval formation, the LCC and UCL subgroups appear not to be truly coeval.