CPD-64°2731: a massive spun-up and rejuvenated high-velocity runaway star
Katkov, I. Y.; Gvaramadze, V. V.; Castro, N.; Langer, N.; Kniazev, A. Y.; Alexashov, D. B.; Maryeva, O. V.
Russia, Czech Republic, South Africa, United States, Germany
Abstract
We report the results of our study of the high-velocity ({≈ }160 km s^{-1}) runaway O star CPD-64°2731 and its associated horseshoe-shaped nebula discovered with the Wide-field Infrared Survey Explorer. Spectroscopic observations with the Southern African Large Telescope and spectral analysis indicate that CPD-64°2731 is a fast-rotating main-sequence O5.5 star with enhanced surface nitrogen abundance. We derive a projected rotational velocity of {≈ }300 km s^{-1} that is extremely high for this spectral type. Its 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 2. These properties suggest that CPD-64°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 the nebula. Instead, we suggest that the binary interaction happened recently, thereby creating the nebula, with a cavity blown by the current fast stellar wind. This inference is supported by our results of 2D numerical hydrodynamic modelling.