Non-synchronous rotation in massive binary systems

Context. Among the binary systems discovered by the spectroscopic monitoring of Southern Galactic O and WN stars, or the OWN Survey, several systems exhibit very different line broadening between their components. Aims. We aim to characterize these binary systems in order to understand the causes behind their markedly different spectral line widths, providing observational clues as to the physical mechanisms at play. Methods. We used new and archival multi-epoch high-resolution optical spectra for the radial velocity analysis and determined the spectroscopic orbits of both components in five systems: HD 57236, HD 93028, HD 101413, HD 151003, and HD 153426. The physical properties of the individual stellar components were determined through quantitative analysis. Using evolutionary models, we estimated the age of the systems and explored their tidal evolution. Results. The systems consist of O+O or O+B stars, with minimum masses ranging from ∼6 M⊙ to 21 M⊙, in young, wide, and fairly eccentric orbits (periods from approximately 22 to 977 d and eccentricities of e > 0.14). The primary and secondary components have a projected rotational velocity ratio of up to 1:7 (∼27 and ∼193 km s−1 in the case of HD 93028), similar to previous binary systems in this series, namely HD 93343 and HD 96264A. Conclusions. The youth and wide orbits of the systems indicate that the non-synchronous rotational nature of their components is a consequence of the stellar formation process, rather than a result of past binary interactions. While the role of binary interactions may be predominant in many cases, it is not a necessary condition to explain the entire observed population of fast rotators.