71 research outputs found
Gas and dust hydrodynamical simulations of massive lopsided transition discs - I. Gas distribution
Motivated by lopsided structures observed in some massive transition discs,
we have carried out 2D numerical simulations to study vortex structure in
massive discs, including the effects of disc self-gravity and the indirect
force which is due to the displacement of the central star from the barycenter
of the system by the lopsided structure. When only the indirect force is
included, we confirm the finding by Mittal & Chiang (2015) that the vortex
becomes stronger and can be more than two pressure scale heights wide, as long
as the disc-to-star mass ratio is >1%. Such wide vortices can excite strong
density waves in the disc and therefore migrate inwards rapidly. However, when
disc self-gravity is also considered in simulations, self-gravity plays a more
prominent role on the vortex structure. We confirm that when the disc Toomre Q
parameter is smaller than pi/(2h), where h is the disc's aspect ratio, the
vortices are significantly weakened and their inward migration slows down
dramatically. Most importantly, when the disc is massive enough (e.g. Q~3), we
find that the lopsided gas structure orbits around the star at a speed
significantly slower than the local Keplerian speed. This sub-Keplerian pattern
speed can lead to the concentration of dust particles at a radius beyond the
lopsided gas structure (as shown in Paper II). Overall, disc self-gravity
regulates the vortex structure in massive discs and the radial shift between
the gas and dust distributions in vortices within massive discs may be probed
by future observations.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Formation, Orbital and Internal Evolutions of Young Planetary Systems
The growing body of observational data on extrasolar planets and
protoplanetary disks has stimulated intense research on planet formation and
evolution in the past few years. The extremely diverse, sometimes unexpected
physical and orbital characteristics of exoplanets lead to frequent updates on
the mainstream scenarios for planet formation and evolution, but also to the
exploration of alternative avenues. The aim of this review is to bring together
classical pictures and new ideas on the formation, orbital and internal
evolutions of planets, highlighting the key role of the protoplanetary disk in
the various parts of the theory. We begin by briefly reviewing the conventional
mechanism of core accretion by the growth of planetesimals, and discuss a
relatively recent model of core growth through the accretion of pebbles. We
review the basic physics of planet-disk interactions, recent progress in this
area, and discuss their role in observed planetary systems. We address the most
important effects of planets internal evolution, like cooling and contraction,
the mass-luminosity relation, and the bulk composition expressed in the
mass-radius and mass-mean density relations.Comment: 49 pages, 12 figures, accepted for publication in Space Science
Reviews. Chapter in International Space Science Institute (ISSI) Book on "The
Disk in Relation to the Formation of Planets and their Proto-atmospheres" to
be published in Space Science Reviews by Springe
Gravito-inertial waves in a differentially rotating spherical shell
The gravito-inertial waves propagating over a shellular baroclinic flow
inside a rotating spherical shell are analysed using the Boussinesq
approximation. The wave properties are examined by computing paths of
characteristics in the non-dissipative limit, and by solving the full
dissipative eigenvalue problem using a high-resolution spectral method.
Gravito-inertial waves are found to obey a mixed-type second-order operator and
to be often focused around short-period attractors of characteristics or
trapped in a wedge formed by turning surfaces and boundaries. We also find
eigenmodes that show a weak dependence with respect to viscosity and heat
diffusion just like truly regular modes. Some axisymmetric modes are found
unstable and likely destabilized by baroclinic instabilities. Similarly, some
non-axisymmetric modes that meet a critical layer (or corotation resonance) can
turn unstable at sufficiently low diffusivities. In all cases, the instability
is driven by the differential rotation. For many modes of the spectrum, neat
power laws are found for the dependence of the damping rates with diffusion
coefficients, but the theoretical explanation for the exponent values remains
elusive in general. The eigenvalue spectrum turns out to be very rich and
complex, which lets us suppose an even richer and more complex spectrum for
rotating stars or planets that own a differential rotation driven by
baroclinicity.Comment: 33 pages, 14 figures, accepted for publication in Journal of Fluid
Mechanic
Using planet migration and dust drift to weigh protoplanetary discs
ALMA has spatially resolved over 200 annular structures in protoplanetary
discs, many of which are suggestive of the presence of planets. Constraining
the mass of these putative planets is quite degenerate for it depends on the
disc physical properties, and for simplicity a steady-state is often assumed
whereby the planet position is kept fixed and there is a constant source of
dust at the outer edge of the disc. Here we argue against this approach by
demonstrating how the planet and dust dynamics can lift degeneracies of such
steady-state models. We take main disc parameters from the well-known
protoplanetary disc HD 163296 with a suspected planet at ~au as an
example. By running gas and dust hydrodynamical simulations post-processed with
dust radiative transfer calculations, we first find steady-state disc and
planet parameters that reproduce ALMA continuum observations fairly well. For
the same disc mass, but now allowing the planet to migrate in the simulation,
we find that the planet undergoes runaway migration and reaches the inner disc
in Myr. Further, decreasing the disc mass slows down planet
migration, but it then also increases the dust's radial drift, thereby
depleting the disc dust faster. We find that the opposing constraints of planet
migration and dust drift require the disc mass to be at most 0.025~\msun,
must less massive than previously estimated, and for the dust to be porous
rather than compact. We propose that similar analysis should be extended to
other sources with suspected planetary companions.Comment: 15 pages, 9 figures, resubmitted to MNRAS, version addressing
referee's comment
The complex interplay between tidal inertial waves and zonal flows in differentially rotating stellar and planetary convective regions:I. Free waves
Quantifying tidal interactions in close-in two-body systems is of prime
interest since they have a crucial impact on the architecture and on the
rotational history of the bodies. Various studies have shown that the
dissipation of tides in either body is very sensitive to its structure and to
its dynamics, like differential rotation which exists in the outer convective
enveloppe of solar-like stars and giant gaseous planets. In particular, tidal
waves may strongly interact with zonal flows at the so-called corotation
resonances, where the wave's Doppler-shifted frequency cancels out. We aim to
provide a deep physical understanding of the dynamics of tidal inertial waves
at corotation resonances, in the presence of differential rotation profiles
typical of low-mass stars and giant planets. By developping an inclined
shearing box, we investigate the propagation and the transmission of free
inertial waves at corotation, and more generally at critical levels, which are
singularities in the governing wave differential equation. Through the
construction of an invariant called the wave action flux, we identify different
regimes of wave transmission at critical levels, which are confirmed with a
one-dimensional three-layer numerical model. We find that inertial waves can be
either fully transmitted, strongly damped, or even amplified after crossing a
critical level. The occurrence of these regimes depends on the assumed profile
of differential rotation, on the nature as well as the latitude of the critical
level, and on wave parameters such as the inertial frequency and the
longitudinal and vertical wavenumbers. Waves can thus either deposit their
action flux to the fluid when damped at critical levels, or they can extract
action flux to the fluid when amplified at critical levels. Both situations
could lead to significant angular momentum exchange between the tidally
interacting bodies.Comment: 25 pages, 12 figures, 4 tables, accepted for publication in Astronomy
& Astrophysic
Rapid inward migration of planets formed by gravitational instability
The observation of massive exoplanets at large separation from their host
star, like in the HR 8799 system, challenges theories of planet formation. A
possible formation mechanism involves the fragmentation of massive
self-gravitating discs into clumps. While the conditions for fragmentation have
been extensively studied, little is known of the subsequent evolution of these
giant planet embryos, in particular their expected orbital migration. Assuming
a single planet has formed by fragmentation, we investigate its interaction
with the gravitoturbulent disc it is embedded in. Two-dimensional
hydrodynamical simulations are used with a simple prescription for the disc
cooling. A steady gravitoturbulent disc is first set up, after which
simulations are restarted including a planet with a range of masses
approximately equal to the clump's initial mass expected in fragmenting discs.
Planets rapidly migrate inwards, despite the stochastic kicks due to the
turbulent density fluctuations. We show that the migration timescale is
essentially that of type I migration, with the planets having no time to open a
gap. In discs with aspect ratio ~ 0.1 at their forming location, planets with a
mass comparable to, or larger than Jupiter's can migrate in as short as 10000
years, that is, about 10 orbits at 100 AU. Massive planets formed at large
separation from their star by gravitational instability are thus unlikely to
stay in place, and should rapidly migrate towards the inner parts of
protoplanetary discs, regardless of the planet mass.Comment: 13 pages, 10 figures, accepted for publication in MNRA
No snow-plough mechanism during the rapid hardening of supermassive black hole binaries
We present two-dimensional hydrodynamical simulations of the tidal
interaction between a supermassive black hole binary with moderate mass ratio,
and the fossil gas disc where it is embedded. Our study extends previous
one-dimensional height-integrated disc models, which predicted that the density
of the gas disc between the primary and the secondary black holes should rise
significantly during the ultimate stages of the binary's hardening driven by
the gravitational radiation torque. This snow-plough mechanism, as we call it,
would lead to an increase in the bolometric luminosity of the system prior to
the binary merger, which could be detected in conjunction with the
gravitational wave signal. We argue here that the snow-plough mechanism is
unlikely to occur. In two-dimensions, when the binary's hardening timescale
driven by gravitational radiation becomes shorter than the disc's viscous drift
timescale, fluid elements in the inner disc get funneled to the outer disc
through horseshoe trajectories with respect to the secondary. Mass leakage
across the secondary's gap is thus found to be effective and, as a result, the
predicted accretion disc luminosity will remain at roughly the same level prior
to merger.Comment: 5 pages, 5 figures, accepted for publication in MNRA
Numerical convergence in self-gravitating disc simulations: initial conditions and edge effects
We study the numerical convergence of hydrodynamical simulations of
self-gravitating accretion discs, in which a simple cooling law is balanced by
shock heating. It is well-known that there exists a critical cooling time scale
for which shock heating can no longer compensate for the energy losses, at
which point the disc fragments. The numerical convergence of previous results
of this critical cooling time scale was questioned recently using Smoothed
Particle Hydrodynamics (SPH). We employ a two-dimensional grid-based code to
study this problem, and find that for smooth initial conditions, fragmentation
is possible for slower cooling as the resolution is increased, in agreement
with recent SPH results. We show that this non-convergence is at least partly
due to the creation of a special location in the disc, the boundary between the
turbulent and the laminar region, when cooling towards a gravito-turbulent
state. Converged results appear to be obtained in setups where no such sharp
edges appear, and we then find a critical cooling time scale of ~ 4
, where is the local angular velocity.Comment: 5 pages, 5 figures, accepted for publication in MNRA
The Disk Substructures at High Angular Resolution Project (DSHARP). VII. The Planet–Disk Interactions Interpretation
The Disk Substructures at High Angular Resolution Project (DSHARP) provides a large sample of protoplanetary disks with substructures that could be induced by young forming planets. To explore the properties of planets that may be responsible for these substructures, we systematically carry out a grid of 2D hydrodynamical simulations, including both gas and dust components. We present the resulting gas structures, including the relationship between the planet mass, as well as (1) the gaseous gap depth/width and (2) the sub/super-Keplerian motion across the gap. We then compute dust continuum intensity maps at the frequency of the DSHARP observations. We provide the relationship between the planet mass, as well as (1) the depth/width of the gaps at millimeter intensity maps, (2) the gap edge ellipticity and asymmetry, and (3) the position of secondary gaps induced by the planet. With these relationships, we lay out the procedure to constrain the planet mass using gap properties, and study the potential planets in the DSHARP disks. We highlight the excellent agreement between observations and simulations for AS 209 and the detectability of the young solar system analog. Finally, under the assumption that the detected gaps are induced by young planets, we characterize the young planet population in the planet mass–semimajor axis diagram. We find that the occurrence rate for \u3e5 M J planets beyond 5–10 au is consistent with direct imaging constraints. Disk substructures allow us to probe a wide-orbit planet population (Neptune to Jupiter mass planets beyond 10 au) that is not accessible to other planet searching techniques
Dust traps in the protoplanetary disc MWC 758: two vortices produced by two giant planets?
Resolved ALMA and VLA observations indicate the existence of two dust traps
in the protoplanetary disc MWC 758. By means of 2D gas+dust hydrodynamical
simulations post-processed with 3D dust radiative transfer calculations, we
show that the spirals in scattered light, the eccentric, asymmetric ring and
the crescent-shaped structure in the (sub)millimetre can all be caused by two
giant planets: a 1.5-Jupiter mass planet at 35 au (inside the spirals) and a
5-Jupiter mass planet at 140 au (outside the spirals). The outer planet forms a
dust-trapping vortex at the inner edge of its gap (at ~85 au), and the
continuum emission of this dust trap reproduces the ALMA and VLA observations
well. The outer planet triggers several spiral arms which are similar to those
observed in polarised scattered light. The inner planet also forms a vortex at
the outer edge of its gap (at ~50 au), but it decays faster than the vortex
induced by the outer planet, as a result of the disc's turbulent viscosity. The
vortex decay can explain the eccentric inner ring seen with ALMA as well as the
low signal and larger azimuthal spread of this dust trap in VLA observations.
Finding the thermal and kinematic signatures of both giant planets could verify
the proposed scenario.Comment: 18 pages, 8 figures, accepted for publication in MNRA
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