{#sec:parmodel}
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We first use a set of parametric models to study the underlying density distribution of mm-sized dust in the system, which we fit directly to the observed visibilities as in [@Marino2016; @Marino2017etacorvi; @Marino201761vir]. Inspired by the radial profile of the dust emission (Figure \[fig:radial\_profile\]), we first choose as a disc model an axisymmetric disc with a surface density that is parametrized as a triple power law that divides the disc into an inner edge, an intermediate section (where the bulk of the dust mass is) and an outer edge. On top of this, the triple power law surface density distribution has a gap, which we parametrise with a Gaussian profile, to reproduce the depression seen in the ALMA data. This parametrization introduces a total of 9 parameters that define the surface density as follows,

$$\begin{aligned}
    &\Sigma(r)=&\Sigma_0 f_\mathrm{gap}(r) \begin{cases}
      \left(\frac{r}{r_{\min}}\right)^{\gamma_1}  & \text{$r<r_{\min}$}, \\
      \left(\frac{r}{r_{\min}}\right)^{\gamma_2}  & \text{$r_{\min}<r<r_{\max}$}, \\
      \left(\frac{r}{r_{\max}}\right)^{\gamma_3}\left(\frac{r_{\max}}{r_{\min}}\right)^{\gamma_2}  & \text{$r>r_{\max}$}, \\
   \end{cases} \label{eq:self-stir}\\
   &f_\mathrm{gap}(r)=& 1-\delta_\mathrm{g}\exp\left[-\frac{(r-r_\mathrm{g})^2}{2\sigma_\mathrm{g}^2}\right],\end{aligned}$$

where ${r_{\min}}$ and ${r_{\max}}$ are the inner and outer radii of the disc, $\gamma_{1,2,3}$ determine how the surface density varies interior to the disc inner radius, within the disc and beyond the disc outer radius. The gap is parametrized with a fractional depth ${\delta_\mathrm{g}}$, 