Testing dust trapping in the circumbinary disk around GG Tau A

Abstract

The protoplanetary disk around the GGTau A binary system is so far one of the most studied young circumbinary disk. Observations of the dust continuum emission at sub-mm/mm wavelengths detected a dust ring located between 200AU and 300AU from the center of mass of the system. If the disk and the binary orbit are coplanar, given the observed projected separation of the stars in the binary system, the classical theory of tidal interaction between a binary system and its circumbinary disk predicts a truncation radius which is significantly smaller than the measured inner radius of the mm-sized dust ring. We investigate the origin of this dust ring structure in the GG Tau A disk, test whether the interaction between the binary and the disk can produce a dust trap at the location of the observed ring, and discuss an alternative scenario which invokes a misalignment between the disk and the stellar orbital planes. We run a set of hydrodynamical simulations for an orbit consistent with the astrometric solutions for the GG Tau A stellar proper motions, and for different disk temperature and viscosities. We then apply a dust evolution model in post-processing in order to to retrieve the distribution of mm-sized grains. Comparing models and observations, we show that, if the binary orbit and the disk were coplanar,the tidal truncation of the circumbinary disk would occur at a radius that is too small compared to the inner edge inferred by the dust observations, and that the pressure bump and the dust ring in the models would be located at <150AU from the center of mass of the stellar system. This shows that the GG Tau A disk cannot be coplanar with the binary orbital plane. 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 degrees.