The coupled effect of tides and stellar winds on the evolution of compact binaries

We follow the evolution of compact binaries under the coupled effect of tides and stellar winds until the onset of Roche lobe overflow. These binaries contain a compact object (either a black hole, a neutron star or a planet) and a stellar component. We integrate the full set of tidal equations, which are based on Hut's model for tidal evolution, and we couple them with the angular momentum loss in a stellar wind. Our aim is twofold. First, we wish to highlight some interesting evolutionary outcomes of the coupling. When tides are coupled with a non-massive stellar wind, one interesting outcome is that in certain types of binaries, the stellar spin tends to reach a quasi-equilibrium state, where the effects of tides and wind are counteracting each other. When tides are coupled with a massive wind, we parametrize the evolution in terms of the decoupling radius, at which the wind decouples from the star. Even for small decoupling radii, this wind braking can drive systems on the main sequence to Roche lobe overflow that otherwise would fail to do so. Our second aim is to inspect whether simple time-scale considerations are a good description of the evolution of the systems. We find that simple time-scale considerations, which rely on neglecting the coupling between tides and stellar winds, do not accurately represent the true evolution of compact binaries. The outcome of the coupled evolution of the rotational and orbital elements can strongly differ from simple time-scale considerations, as already pointed out by Barker and Ogilvie in the case of short-period planetary systems.status: publishe