We investigate whether the rings , lopsided features and horseshoes observed at millimetre wavelengths in transitional discs can be explained by the dynamics of gas and dust at the edge of the cavity in circumbinary discs .
We use 3D dusty smoothed particle hydrodynamics calculations to show that binaries with mass ratio q \gtrsim 0.04 drive eccentricity in the central cavity , naturally leading to a crescent-like feature in the gas density , which is accentuated in the mm dust grain population with intensity contrasts in mm-continuum emission of 10 or higher .
We perform mock observations to demonstrate that these features closely match those observed by ALMA , suggesting that the origin of rings , dust horseshoes and other non-axisymmetric structures in transition discs can be explained by the presence of massive companions .