Dust rings formation in misaligned circumbinary discs

In many cases the result of molecular cloud collapse is a binary (or multiple) stellar system. In particular, if the collapse is forming a binary system, three discs can be formed: two around the stars (circumprimary and circumsecundary) and a larger disc surrounding both the stars, called circumbinary.
Here I present an analytical and numerical study of dust rings formation in misaligned circumbinary discs. In my work, I found that pile-ups of dust may be induced not only by pressure maxima, as the usual dust traps, but also by a difference in precession rates between the gas and dust. I considered a disc composed of gas and dust; I assumed that the gas precesses as a rigid body, thanks to the viscosity, while the dust differentially precesses because of its viscousless and pressureless nature.
The net effect of the aerodynamical coupling between the two components is the so called “radial drift”, i.e. the dust acquires a negative radial velocity and migrate towards the central object. This force does not act whenever the difference of speed is equal to zero. Projecting the dusty velocity field onto the gaseous plane I found two radii - an inner and outer dust radius- at which the difference of speed between gas and dust is zero. At these locations, the dust, that is migrating from the outer part of the disc because of radial drift, piles up, leading to the formation of dusty rings. The position of the rings depends on a series of parameters defining the disc, as its radial extent, its density profile and its thickness. To confirm my theoretical predictions, I performed numerical simulations using the SPH code PHANTOM: I used the two fluid algorithm because I was interested in the marginally coupled regime. By means of these simulations I explored the parameter space as much as possible: I found an overall general agreement between the results of the simulations and the analytical expectations, with some discrepancies that can be related to the specific hypothesis I have made. This mechanism could be significant in the context of planetary formation in binary stellar systems because these traps could foster the dust coagulation and the formation of planetesimals.