CPD−64 2731: a massive spun-up and rejuvenated high-velocity runaway star

During our search for massive stars on late evolutionary stages in the WISE archive we discovered a high-velocity runaway star CPD-64o 2731, associated with a horseshoe-shaped nebula. Its spectral type is O5.5Vn((f)) and projected rotational velocity is ≈ 300 km/s, which is extremely high for this spectral type. The kinematic age of ≈ 6 Myr, assuming it was born near the Galactic plane, exceeds its age derived from single star models by a factor of two. These properties suggest that CPD-64o 2731 is a rejuvenated and spun-up binary product. The geometry of the nebula and the almost central location of the star within it argue against a pure bow shock interpretation for it. Instead, we suggest that the binary interaction happened recently, thereby creating the nebula, with a cavity blown by the current fast stellar wind. This conclusion is supported by our results of 2D numerical hydrodynamic modeling.