Dust concentration and emission in protoplanetary disks vortices [EPA]


We study dust concentration and emission within vortices in protoplanetary disks. We extend the Lyra-Lin solution for the dust concentration of a single grain size to a power-law distribution of grain sizes $n(a) \propto a^{-p}$. Assuming dust conservation in the disk, we find an analytic dust surface density as a function of the grain radius. We calculate increase in the dust to gas mass ratio $\epsilon$ and the slope $p$ of the dust size distribution due to grain segregation within the vortex. We apply this model to a numerical simulation of a disk containing a persistent vortex. Due to the accumulation of large grains towards the vortex center, $\epsilon$ reaches values $\sim 0.1$, while the slope decreases to $p \sim 3.0$ (from initial values of $\epsilon=0.0131$ and $p=3.5$, respectively). We find the disk emission at millimeter wavelengths corresponding to synthetic observations with ALMA and VLA. The simulated maps at 7 mm and 1 cm show a strong azimuthal asymmetry. The emission contrast between the disk and the vortex is produced because, at these wavelengths, the disk becomes optically thin while the vortex remains optically thick. The large opacity in the vortex is mainly due to an increase in the dust to gas mass ratio. In addition, the change in the slope of the dust size distribution increases the opacity by a factor of 2. We also show that the inclusion of scattering substantially changes the disks images.

Read this paper on arXiv…

A. Sierra, S. Lizano and P. Barge
Wed, 11 Oct 17

Comments: 13 pages, 20 figures