arXiv subjects

Thomas Rometsch

Publications and source records attributed to Thomas Rometsch.

6 recordsLinked to original sources

arXiv2026

Formation of multiple dust rings and gaps in protoplanetary discs by a single migrating planet. A parameter study in locally isothermal discs

ALMA observations show that large protoplanetary discs usually contain multiple concentric dust rings separated by dark gaps. A natural explanation is dust-trapping at the edges of gaps opened by newly formed planets. However, planets typically migrate inward on timescales shorter than disc lifetimes, seemingly at odds with rings at large radii. We aim to investigate the conditions under which migrating planets can form long-lived, multi-ringed structures out to $r\sim 150$ au to constrain the parameter space for the planetary origin hypothesis of rings. Using the FargoCPT hydrodynamics code, we ran two-dimensional, locally isothermal disc models with a single migrating planet, varying disc aspect ratio, viscosity ($\alpha$), and planetary mass. In all models, the planet eventually stalls in a deep gap. At $\alpha\leq 10^{-4}$, secondary spirals launched by the planet can open additional gaps at smaller radii. When planets exceed twice the local thermal mass before stalling, they enter a regime of alternating slow and type-III rapid migration, leaving partial gaps outside their orbit. The gap edges consistently feature pressure maxima that trap dust. These begin as large vortices at $\alpha\leq 10^{-4}$, but gradually smear out into rings before dissipating. The type-III remnant rings dissipate quickly at $\alpha=10^{-3}$, but persist for at least 300-500 kyr at $\alpha\leq 10^{-4}$. Both smear-out and dissipation timescales increase with lower $\alpha$. Our results show that migrating planets can reproduce observed multi-ringed structures in discs with $\alpha\lesssim 10^{-4}$ through their stall ($r\lesssim 50$ au), secondary gap-opening ($r\lesssim 20$ au), and type-III migration remnants (extending to $r\sim 150$ au for Jupiter-mass planets in sufficiently massive discs). Longer simulations will be required to compare the statistics of ring-to-vortex occurrence to observations.

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arXiv2024

Hydrodynamical simulations with strong indirect terms in Fargo-like codes: Numerical aspects of non-inertial frame and artificial viscosity

Context. Binary star systems allow us to study the planet formation process under extreme conditions. In the early stages, these systems contain a circumbinary disk and a disk around each star. To model the interactions between these disks in the frame of one of the stars, strong fictitious forces must be included in the simulations. The original Fargo and the Fargo3D codes fail to correctly simulate such systems if the indirect term becomes too strong. Aims. We present a different way to compute the indirect term which, together with a tensor artificial viscosity prescription, allows the Fargo code to simulate the circumbinary disks in a non-inertial frame of reference. In this way, the Fargo code can be used to study interactions between circumstellar and circumbinary disks. Results. We find that updating the indirect term becomes relevant when the indirect term becomes stronger than the direct gravitational forces, which occurs for mass ratios of $q > 5\%$. The default artificial viscosity used in the Fargo code inherently produces artificial pressure in a non-inertial frame of reference even in the absence of shocks. This leads to artificial mass ejection from the Hill sphere, starting at brown dwarf masses ($q > 1\%$). These problems can be mitigated by using a tensor artificial viscosity formulation. For high mass ratios, $q > 1\%$, it is also becomes important to initialize the disk in the center-of-mass frame. We expect our proposed changes to be relevant for other grid-based hydrodynamic codes where strong indirect terms occur, or for codes that use artificial viscosity.

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arXiv2024

FargoCPT: A 2D Multi-Physics Code for Simulating the Interaction of Disks with Stars, Planets and Particles

Context: Planet-disk interactions play a crucial role in the understanding of planet formation and disk evolution. There are multiple numerical tools available to simulate these interactions, including the often-used FARGO code and its variants. Many of the codes were extended over time to include additional physical processes with a focus on their accurate modeling. Aims: We introduce FargoCPT, an updated version of FARGO incorporating other previous enhancements to the code, to provide a simulation environment tailored to study interactions between stars, planets, and disks, ensuring accurate representation of planet systems, hydrodynamics, and dust dynamics with a focus on usability. Methods: The radiation-hydrodynamics part of FargoCPT uses a second-order upwind scheme in 2D polar coordinates supporting multiple equations of state, radiation transport, heating and cooling, and self-gravity. Shocks are considered using artificial viscosity. Integration of the N-body system is achieved by leveraging the REBOUND code. The dust module utilizes massless tracer particles, adapting to drag laws for the Stokes and Epstein regimes. Moreover, FargoCPT provides mechanisms to simulate accretion onto the stars and planets. Results: The code has been tested in practice by its use in various publications. Additionally, it comes with an automated test suite to test the physics modules. Conclusions: FargoCPT offers a unique set of simulation capabilities within the current landscape of publicly available planet-disk interaction simulation tools. Its structured interface and underlying technical updates are intended to assist researchers in the ongoing exploration of planet formation.

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arXiv2021

Survival of planet-induced vortices in 2D disks

Context: Several observations of protoplanetary disks display non-axisymmetric features, often interpreted as vortices. Numerical modeling has repeatedly shown that gap-opening planets are capable of producing large and long-lasting vortices at their outer gap edge, making massive planets popular candidates as the source of such features. Aims: We explore the lifetime of vortices generated by Jupiter-sized planets as a function of the thermal relaxation timescale, the level of turbulence, and the effect of disk self-gravity. Methods: We conduct 2D numerical simulations using the hydrodynamics codes PLUTO and FARGO, scanning through several physical and numerical parameters. Vortex properties are automatically extracted from thousands of simulation snapshots. Results: We find that vortices that spawn at the outer gap edge can survive for about 100-3000 planetary orbits, with the shortest lifetimes occurring for moderately efficient dissipation and cooling. However, we also observe a different regime of long-lasting vortices with lifetimes of at least 15 000 orbits for very low viscosity and very short thermal relaxation timescales. Disk self-gravity significantly shortens the lifetime of regular vortices but still allows long-lived ones to survive. Conclusions: Our results suggest that the cooling timescale plays an important role in vortex formation and lifetime and that planet-generated vortices should be observable at large distances from the star for typical thermal relaxation timescales and low turbulence levels.

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arXiv2020

Modeling the nonaxisymmetric structure in the HD 163296 disk with planet-disk interaction

High resolution ALMA observations revealed a variety of rich substructures in numerous protoplanetary disks. These structures consist of rings, gaps and asymmetric features. It is debated whether planets can be accounted for these substructures in the dust continuum. Characterizing the origin of asymmetries as seen in HD 163296 might lead to a better understanding of planet formation and the underlying physical parameters of the system. We test the possibility of the formation of the crescent-shaped asymmetry in the HD 163296 disk through planet-disk interaction. The goal is to obtain constraints on planet masses and eccentricities and disk viscosities. Two dimensional, multi-fluid, hydrodynamical simulations are performed with the FARGO3D code including three embedded planets. Dust is described with the pressureless fluid approach and is distributed over eight size bins. Resulting grids are post-processed with the radiative transfer code RADMC-3D and the CASA software to model synthetic observations. We find that the crescent-shaped asymmetry can be qualitatively modeled with a Jupiter mass planet at a radial distance of 48 au. Dust is trapped preferably in the trailing Lagrange point L5 with a mass of 10 to 15 earth masses. Increased values of eccentricity of the innermost Jupiter mass planet damages the stability of the crescent-shaped feature and does not reproduce the observed radial proximity to the first prominent ring in the system. Generally, a low level of viscosity ($α\leq 2\cdot10^{-3}$) is necessary to allow the existence of such a feature. Including dust feedback the leading point L4 can dominantly capture dust for dust grains with an initial Stokes number $\leq 3.6\cdot 10^{-2}$. The observational results suggest a negligible effect of dust feedback since only one such feature has been detected so far.

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arXiv2020

Migration jumps of planets in transition disks

Transition disks form a special class of protoplanetary disks that are characterized by a deficiency of disk material close to the star. In a subgroup, inner holes in these disks can stretch out to a few tens of au while there is still mass accretion onto the central star observed. We analyse the proposition that this type of wide transition disks is generated by the interaction of the disk with a system of embedded planets. We performed 2D hydrodynamics simulations of a flat disk using either a locally isothermal equation of state or considering also radiative effects. Two 3 to 9 Jupiter mass planets were embedded in the disk and their dynamical evolution due to disk-planet interaction was followed for over 100 000 years. The simulations account for mass accretion onto the star and planets. We included models with parameters geared to the system PDS 70. To assess the observability of features in our models we performed synthetic ALMA observations. For systems with a more massive inner planet there are phases where both planets migrate outward engaged in a 2:1 mean motion resonance via the Masset-Snellgrove mechanism. In sufficiently massive disks the formation of a vortex in the outer disk can trigger rapid outward migration of the outer planet where its distance increases by tens of au within a few thousand years. Later, the outer planet migrates back inwards settling again into resonance with the inner planet. We call this emerging composite phenomenon a 'migration jump'. Outward migration and the migration jumps are accompanied by a high mass accretion rate onto the star. The synthetic images reveal numerous substructures depending on the type of dynamical behaviour. Our results suggest that the outward migration of two embedded planets is a prime candidate for the explanation of the observed high stellar mass accretion rate in wide transition disks.

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