26 research outputs found
Dust capture and long-lived density enhancements triggered by vortices in 2D protoplanetary disks
We study dust capture by vortices and its long-term consequences in global
two-fluid inviscid disk simulations using a new polar grid code RoSSBi. We
perform the longest integrations so far, several hundred disk orbits, at the
highest resolution attainable in global simulations of disks with dust, namely
2048x4096 grid points. This allows to study the dust evolution well beyond
vortex dissipation. We vary a wide range of parameters, most notably the
dust-to-gas ratio in the initial setup varies in the range to .
Irrespective of the initial dust-to-gas ratio we find rapid concentration of
the dust inside vortices, reaching dust-to-gas ratios of order unity inside the
vortex. We present an analytical model that describes very well the dust
capture process inside vortices, finding consistent results for all dust-to-gas
ratios. A vortex streaming instability develops which causes invariably vortex
destruction. After vortex dissipation large-scale dust-rings encompassing a
disk annulus form in most cases, which sustain very high dust concentration,
approaching ratios of order unity. The rings are long lived lasting as long as
the duration of the simulations. They also develop a streaming instability,
which manifests itself in eddies at various scales within which the dust forms
compact high density clumps. Such clumps would be unstable to gravitational
collapse in absence of strong dissipation by viscous forces. When vortices are
particularly long lived, rings do not form but dust clumps inside vortices
become then long lived features and would likely undergo collapse by
gravitational instability. Rings encompass almost an Earth mass of solid
material, while even larger masses of dust do accumulate inside vortices in the
earlier stage. We argue that rapid planetesimal formation would occur in the
dust clumps inside the vortices as well as in the post-vortex ring.Comment: Preprint version, submitted to the Astrophysical Journal. Due to size
constraints on ArXiv, some plots are at low resolution JPEG
Meridional Circulation of Dust and Gas in the Circumstellar Disk: Delivery of Solids onto the Circumplanetary Region
We carried out 3D dust+gas radiative hydrodynamic simulations of forming
planets. We investigated a parameter grid of Neptune-, Saturn-, Jupiter-, and 5
Jupiter-mass planets at 5.2, 30, 50 AU distance from their star. We found that
the meridional circulation \citep{Szulagyi14,FC16} drives a strong vertical
flow for the dust as well, hence the dust is not settled in the midplane, even
for mm-sized grains. The meridional circulation will deliver dust and gas
vertically onto the circumplanetary region, efficiently bridging over the gap.
The Hill-sphere accretion rates for the dust are to
, increasing with planet-mass. For the gas component, the gain
is to . The difference between the dust
and gas accretion rates is smaller with decreasing planetary mass. In the
vicinity of the planet, the mm-grains can get trapped easier than the gas,
which means the circumplanetary disk might be enriched with solids in
comparison to the circumstellar disk. We calculated the local dust-to-gas ratio
(DTG) everywhere in the circumstellar disk and identified the altitude above
the midplane where the DTG is 1, 0.1, 0.01, 0.001. The larger the planetary
mass, the higher the mm-sized dust is delivered and a larger fraction of the
dust disk is lifted by the planet. The stirring of mm-dust is negligible for
Neptune-mass planets or below, but significant above Saturn-mass.Comment: ApJ accepte
AGN disks and black holes on the weighting scales
We exploit our formula for the gravitational potential of finite size,
power-law disks to derive a general expression linking the mass of the black
hole in active galactic nuclei (AGN), the mass of the surrounding disk, its
surface density profile (through the power index s), and the differential
rotation law. We find that the global rotation curve v(R) of the disk in
centrifugal balance does not obey a power law of the cylindrical radius R
(except in the confusing case s = -2 that mimics a Keplerian motion), and
discuss the local velocity index. This formula can help to understand how, from
position-velocity diagrams, mass is shared between the disk and the black hole.
To this purpose, we have checked the idea by generating a sample of synthetic
data with different levels of Gaussian noise, added in radius. It turns out
that, when observations are spread over a large radial domain and exhibit low
dispersion (standard deviation less than 10% typically), the disk properties
(mass and s-parameter) and black hole mass can be deduced from a non linear fit
of kinematic data plotted on a (R, Rv 2)-diagram. For a deviation higher than
10%, masses are estimated fairly well from a linear regression (corresponding
to the zeroth-order treatment of the formula), but the power index s is no
longer accessible. We have applied the model to 7 AGN disks whose rotation has
already been probed through water maser emission. For NGC3393 and UGC3789, the
masses seem well constrained through the linear approach. For IC1481, the
power-law exponent s can even be deduced. Because the model is scale-free, it
applies to any kind of star/disk system. Extension to disks around young stars
showing deviation from Keplerian motion is thus straightforward.Comment: accepted for publication in A&