Non-synchronous rotations in massive binary systems. HD93343 revisited

TL;DR

This study investigates the binary system HD 93343, revealing two similar massive stars with different rotational velocities, suggesting intrinsic formation differences rather than tidal effects or mass transfer.

Contribution

It provides detailed orbital and stellar parameters for HD 93343, highlighting the intrinsic origin of non-synchronous rotation in massive binary stars.

Findings

Both stars are young, massive, and in a wide eccentric orbit.

The stars have significantly different projected rotational velocities.

Tidal forces and mass transfer are unlikely causes of their rotation differences.

Abstract

Context. Most massive stars are in binary or multiple systems. Several massive stars have been detected as doublelined spectroscopic binaries and among these, the OWN Survey has detected a non-negligible number whose components show very different spectral line broadening (i.e., projected rotational velocities). This fact raises a discussion about the contributing processes, such as angular-momentum transfer and tidal forces. Aims. We seek to constrain the physical and evolutionary status of one of such systems, the O+O binary HD 93343. Methods. We analyzed a series of high-resolution multiepoch optical spectra to determine the orbital parameters, projected rotational velocities, and evolutionary status of the system. Results. HD 93343 is a binary system comprised of two O7.5 Vz stars that each have minimum masses of approximately 22 Mo in a wide and eccentric orbit (e = 0.398$\pm$0.004; P=50.432$\pm$0.001 d). Both stars have very similar stellar parameters, and hence ages. As expected from the qualitative appearance of the combined spectrum of the system, however, these stars have very different projected rotational velocities (~65 and ~325 km/s, respectively). Conclusions. The orbits and stellar parameters obtained for both components seem to indicate that their youth and relative separation is enough to discard the effects of mass transfer and tidal friction. Thus, non-synchronization should be intrinsic to their formation.