Radial profiles of pressure (black), gas surface density (red), and dust surface density (blue) for the DHSARP ring B77, from Dullemond et al. (2018) – see Sect. 3. The vertical scale of each profile has been renormalized for illustrative purposes. The dashed thin red curves show the profiles r^2.55 and 1∕r, and their tangential points to the red solid curve shows the locations where the gas surface density profile haslocally these profiles. These two locations delimit the range of possible positions of the planet at the migration trap, depending on the degree of saturation of the vortensity-driven corotation torque. Their distances relative to the location of the pressure maximum are given in terms of the parameter δ, as well as the location of the maximum of the gas surface-density distribution. The widths w and w_d in Eqs. (1) and (4) are also graphically represented.