On the secular evolution of GG Tau A circumbinary disc: A misaligned disc scenario

Abstract

The binary system GG Tau A is observed to have a circumbinary disc with a dust ring located further out than expected, assuming a co-planar disc and a corresponding semimajor axis of 34 au. Given the binary separation, this large cavity can be explained by relaxing the assumption of a co-planar disc and instead fit the observations with a misaligned circumbinary disc around an eccentric binary with a wider semimajor axis of 60 au, consistent with fitting the proper motion data for the system. We run smoothed particle hydrodynamic simulations to check this possibility and indeed we find that a misalignment angle of 30° and a binary eccentricity of 0.45 fit both the astrometric data and the disc cavity. However, such configuration could in principle be unstable to polar, rather that planar alignment. We investigate the secular evolution of this configuration and show that it is indeed stable throughout the disc lifetime.