Dynamical tides in binaries: Inconsistencies in the implementation of Zahn’s prescription

Abstract

Binary evolution codes are essential tools to help in understanding the evolution of binary systems. They contain a great deal of physics, for example stellar evolution, stellar interactions, mass transfer, tides, orbital evolution. Since many of these processes are difficult to account for in detail, we often rely on prescriptions obtained in earlier studies. We highlight that the impact of the dynamical tides with radiative damping has been implemented inconsistently with respect to its original theoretical formulation in many studies. We derive a new analytical solution for the evolution toward synchronization in the case of circular orbits and propose turnkey equations for the case of eccentric orbits that can be used in population synthesis studies. We compare the strength of the tidal torque obtained with this new formula with respect to that obtained with the formula generally used in literature by studying how the evolution toward synchronization of main sequence stellar models is affected. We conclude that by using an incorrect formula for the tidal torque, as has been done in many binary codes, the strength of the dynamical tides with radiative damping is over- or underestimated depending on whether the star is close to or far from synchronization.