2008A&A...485L..29G

The astrometric data on the runaway star BD+43°3654 are consistent with the origin of this O4If star in the center of the Cyg OB2 association, while BD+43°3654 is younger than the association. To reconcile this discrepancy, we suggest that BD+43°3654 is a blue straggler formed via a close encounter between two tight massive binaries in the core of CygOB2. A possible implication of this suggestion is that the very massive (and therefore apparently very young) stars in CygOB2 could be blue stragglers as well. We also suggest that the binary-binary encounter producing BD+43°3654 might be responsible for ejection of two high-velocity stars (the stripped helium cores of massive stars) - the progenitors of the pulsars B2020+28 and B2021+51.