  We fit an isothermal oscillatory density model to two ALMA/DSHARP-observed
disks, AS 209 and HL Tau, in which planets have presumably already formed and
they are orbiting within the observed seven dark gaps in each system. These
large disks are roughly similar to our solar nebula, albeit they exhibit milder
radial density profiles and they enjoy lower centrifugal support. We find
power-law density profiles with index $k=0.0$ (radial densities $\rho(R)
\propto R^{-1}$) and centrifugal support against self-gravity so small that it
guarantees dynamical stability for millions of years of evolution. The scale
lengths of the models differ only by a factor of 1.9, but the inner cores of
the disks are very different: HL Tau's core is 8.0 times larger and 3.6 times
denser than the core of AS 209. This results in four dark gaps having formed
within the core of HL Tau, whereas no dark gap is found in the core of AS 209.
On the other hand, the Jeans frequencies and the angular velocities of the
cores are comparable to within factors of 1.9 and 1.6, respectively.
