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tokens: The astronomical silicates and carbons are assumed from Draine ( 2003 ). The grain size distribution has a slope of −3.5 and goes from 0.03 μ m to 3 mm. To irradiate the disk the star is treated as an isotropic source with stellar spectral models obtained from the 5 Myr isochrones from Siess et al. ( 2000 ), with T eff ∼ 8000 K and a radius R ∼ 2.2 R ⊙ . The source is located at the distance of 117 pc, adopting the disk inclination and position angle of 13° and 5°. 3. Results Our reference profile for the gas and dust distributions is the DALI thermochemical model from FD17 , that models the dust surface density profile Σ dust with two dust rings (20–35 au and 56–83 au) and the gas density profiles Σ gas with an inner cavity (13–56 au) reduced by a factor 30–40. However, we considered an update of the published model of FD17 , limited by the spatial resolution of the available data at the time. Based on the 13 CO J = 3–2 ALMA archive data from Honda et al. ( 2012 ), the gas cavity appears to be located at ∼20–56 au. Figure 1 shows the temporal evolution of the dust and gas surface density profiles, Σ dust and Σ gas , in our simulation. Going from black to red, Σ dust and Σ gas are displayed as a function of time, that we recall is normalized to the orbital period of the outer planet at the initial position (55 au, T orb ∼ 320 yr). Figure 1. Σ dust (top panel) and Σ gas (bottom panel) as a function of the radius R for increasing time. The initial surface density profiles are in black. Our time unit is normalized with the initial orbital period of the outer planet (∼320 yr). The inner planet carves a cavity in the dust and in the gas, with a depletion factor of ∼10 −4 and ∼10 −1 , respectively, inward of its orbit. The outer planet first migrates (see Figure 2 ) while accreting the material, then opens a gap in dust and gas (with depletion factor ∼10 −4 and ∼10 −1 , respectively, in dust and gas) at his “equilibrium” location. The dust ring produced between the two planets is preserved for at least ∼500 orbits, i.e., for over ∼2 × 10 5 yr. At the same time, the gas is accreted on the star and the planets. The density profiles of the gas and dust in our simulation are due to a combination of factors. For the gas, the “cavity” is produced by the torques exerted by the outer planet onto the disk, which prevents the gas outside the outer planet to refill the inner regions that are emptied by viscous accretion. For the dust, the two prominent rings are created by the usual trapping at pressure maxima (indeed, we have verified that the ring location coincides exactly with pressure maxima). This generates a gas cavity with a width of ∼50 au, lowering the gas surface density and increasing the value of the Stokes number that quickly becomes larger than unity, helping the dust trapping due to the pressure gradient in preventing the dust migration and thus preserving the dust ring. Figure 2. Dynamics of the two planets. Top-right panel: the