Testing dust trapping in the circumbinary disk around GG Tauri A

Context. The protoplanetary disk around the GG Tau A binary system is one of the most studied young circumbinary disk, and it has been observed at many different wavelengths. Observations of the dust continuum emission at sub-mm/mm wavelengths have detected a dust ring located between 200 AU and 300 AU from the center of mass of the system. According to the classical theory of tidal interaction between a binary system and its circumbinary disk, the measured inner radius of the mm-sized dust ring is significantly larger than the predicted truncation radius, given the observed projected separation of the stars in the binary system (0.2500, corresponding to ∼34 AU). A possible explanation for this apparent tension between observations and theory is that a local maximum in the gas radial pressure is created at the location of the center of the dust ring in the disk as a result of the tidal interaction with the binary. An alternative scenario invokes the presence of a misalignment between the disk and the stellar orbital planes. Aims. We investigate the origin of this dust ring structure in the GG Tau A circumbinary disk, test whether the interaction between the binary and the disk can produce a gas pressure radial bump at the location of the observed ring, and discuss whether the alternative hypothesis of a misaligned disk offers a more viable solution. Methods. We run a set of 3D hydrodynamical simulations for an orbit consistent with the astrometric solutions for the GG Tau A stellar proper motions, different disk temperature profiles, and for different levels of viscosity. Using the obtained gas surface density and radial velocity profiles, we then apply a dust evolution model in post-processing in order to to retrieve the expected distribution of mm-sized grains. Results. We compare the results of our models with the observational results and show that, if the binary orbit and the disk were coplanar, not only would the tidal truncation of the circumbinary disk occur at a radius that is too small with respect to the inner edge inferred by the dust observations – which is in agreement with classical theory of tidal truncation − but also that the pressure bump and the dust ring in the models would be located at <150 AU from the center of mass of the stellar system. This shows that the GG Tau A circumbinary disk cannot be coplanar with the orbital plane of the binary. We also discuss the viability of the misaligned disk scenario, suggesting that in order for dust trapping to occur at the observed radius, the disk and orbital plane must be misaligned by an angle of about 25−30 degrees.