Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations

By M. Flock, J. P. Ruge, N. Dzyurkevich, Th. Henning, H. Klahr, S. Wolf. 2014

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Aims. Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of disks around young stars revealed distinct asymmetries in the dust continuum emission. In this work we wish to study axisymmetric and non-axisymmetric structures that are generated by the magneto-rotational instability in the outer regions of protoplanetary disks. We combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (RT) to generate synthetic maps and predictions for ALMA.Methods. We performed non-ideal global 3D magneto-hydrodynamic (MHD) stratified simulations of the dead-zone outer edge using the FARGO MHD code PLUTO. The stellar and disk parameters were taken from a parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of various circumstellar disks. We considered a stellar mass of M∗ = 0.5 M⊙ and a total disk mass of about 0.085 M∗. The 2D initial temperature and density profiles were calculated consistently from a given surface density profile and Monte Carlo radiative transfer. The 2D Ohmic resistivity profile was calculated using a dust chemistry model. We considered two values for the dust-to-gas mass ratio, 10-2 and 10-4, which resulted in two different levels of magnetic coupling. The initial magnetic field was a vertical net flux field. The radiative transfer simulations were performed with the Monte Carlo-based 3D continuum RT code MC3D. The resulting dust reemission provided the basis for the simulation of observations with ALMA.Results. All models quickly turned into a turbulent state. The fiducial model with a dust-to-gas mass ratio of 10-2 developed a large gap followed by a jump in surface density located at the dead-zone outer edge. The jump in density and pressure was strong enough to stop the radial drift of particles at this location. In addition, we observed the generation of vortices by the Rossby wave instability at the jump location close to 60 AU. The vortices were steadily generated and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA observations predict that it is feasible to observe these large-scale structures that appear in magnetized disks without planets. Neither the turbulent fluctuations in the disk nor specific times of the model can be distinguished on the basis of high-angular resolution submillimeter observations alone. The same applies to the distinction between gaps at the dead-zone edges and planetary gaps, to the distinction between turbulent and simple unperturbed disks, and to the asymmetry created by the vortex.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/20930c3caed94759933b0e6f7aa07aad1b4a709e

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Citations in the corpus

ALMA unveils rings and gaps in the protoplanetary system HD 169142: signatures of two giant protoplanets (2017, background): “An alternative scenario that could also explain the surface density profile of HD 169142 is the case of magneto-rotational (MRI) instability creating dead-zones (e.g., Regály et al. 2012; Flock et al. 2015; Hasegawa & Takeuchi 2015).”
Kinematic Evidence for an Embedded Protoplanet in a Circumstellar Disk (2018, background): “This excludes, for example, ice lines (Zhang et al. 2015), self-induced dust traps (Gonzalez et al. 2015), instabilities (Takahashi & Inutsuka 2014; Lorén-Aguilar & Bate 2015) and zonal flows (Flock et al. 2015).”
The Disk Substructures at High Angular Resolution Project (DSHARP). I. Motivation, Sample, Calibration, and Overview (2018, background): “…could be produced by the dynamics associated with how gas, dust, and magnetic fields are coupled (e.g., Dzyurkevich et al. 2013; Bai & Stone 2014; Flock et al. 2015; Lyra et al. 2015; Dipierro et al. 2015; Béthune et al. 2017; Dullemond & Penzlin 2018; Suriano et al. 2018) or by strong…”
EVIDENCE OF FAST PEBBLE GROWTH NEAR CONDENSATION FRONTS IN THE HL TAU PROTOPLANETARY DISK (2015, background): “…Pasadena, CA 91125, USA 3 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109, USA bilities that form planetesimals (Kretke & Lin 2007; Brauer et al. 2008; Ros & Johansen 2013; Bitsch et al. 2014; Dra̧żkowska & Dullemond 2014; Flock et al. 2015).”
Close-in planetesimal formation by pile-up of drifting pebbles (2016, methodology): “In the models presented in this paper, we do not include processes, such as zonal flows that may potentially create pressure bumps in the outer parts of the disc (Flock et al. 2015).”
The Disk Substructures at High Angular Resolution Project (DSHARP). II. Characteristics of Annular Substructures (2018, background): “Absent a direct detection of a planet, it is not observationally straightforward to distinguish between planet-disk interactions and magnetohydrodynamic effects (e.g., Flock et al. 2015; Ruge et al. 2016).”
The Disk Substructures at High Angular Resolution Project (DSHARP). VII. The Planet–Disk Interactions Interpretation (2018, background): “…mechanisms to produce gaps and rings, such as ice lines (Zhang et al. 2015; Okuzumi et al. 2016), the dead zone transition (Pinilla et al. 2016), MHD zonal flows (Flock et al. 2015; Ruge et al. 2016), the secular GI (Takahashi & Inutsuka 2014), disk winds (Bai 2017; Suriano et al. 2018), and so on.”
Three Radial Gaps in the Disk of TW Hydrae Imaged with SPHERE (2016, background): “Also non-ideal MRI-based simulations yield radial depressions in the gas surface density (Flock et al. 2015; Ruge et al. 2016).”
On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening (2017, background): “As for the gaseous counterparts to these stellar disks, AGN disks may be messy, sharing the large-scale structures evident in high resolution observations of protoplanetary disks (e.g. van der Marel et al. 2013; Pérez et al. 2014; Casassus et al. 2013; Flock et al. 2015).”
RINGED SUBSTRUCTURE AND A GAP AT 1 au IN THE NEAREST PROTOPLANETARY DISK (2016, background): “Ring and gap features have also been found in simulations that consider the dynamical effects of radial variations in the disk resistivity (e.g., Flock et al. 2015; Lyra et al. 2015).2 Overall, low-amplitude radial surface density variations may be a generic consequence of magnetized disk evolution.”
Gaps and Rings in an ALMA Survey of Disks in the Taurus Star-forming Region (2018, background): “Pressure bumps could be created outside the orbit of a planet (e.g., Pinilla et al. 2012b) or the outer edge of a low-ionization region (the so-called dead zone; Flock et al. 2015).”
A Kinematical Detection of Two Embedded Jupiter-mass Planets in HD 163296 (2018, background): “An alternative solution for this perturbation is the pressure confinement of grains at 80 au due to the edge of the deadzone of the magnetorotational instability (Flock et al. 2015; Pinilla et al. 2016).”
Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights (2021, background): “The observed gaps have often been connected to ongoing planet formation (e.g., Flock et al. 2015; Fedele et al. 2017; Keppler et al. 2019), though other plausible explanations exist as well (see Andrews 2020, for a review).”
Dust Evolution and the Formation of Planetesimals (2016, background): “Other proposed explanations include pressure bumps formed due to magnetised turbulence (Johansen et al. 2009; Dittrich et al. 2013; Flock et al. 2015) or condensation fronts (Cuzzi & Zahnle 2004; Ros & Johansen 2013; Zhang et al. 2015; Okuzumi et al. 2015).”
Measuring turbulence in TW Hydrae with ALMA: methods and limitations (2016, background): “Flock et al. (2015) ran similar, however global, models of an MRI active disk, finding velocity dispersions of vturb ≈ 40 – 60 m s−1 near the midplane, rising to 80 – 120 m s−1 higher above the midplane, again consistent with the values found in TW Hya.”
Shadows and spirals in the protoplanetary disk HD 100453 (2016, background): “These rings indicated that planet formation might occur very early in the disk lifetime, but alternative explanations, such as hydrodynamical instabilities were also proposed (Flock et al. 2015; Ruge et al. 2016; Béthune et al. 2016).”
ALMA continuum observations of the protoplanetary disk AS 209. Evidence of multiple gaps opened by a single planet (2017, background): “…formation of gaps and rings in disks can be due to several mechanisms such as: planet formation (e.g., Papaloizou & Lin 1984); magneto-rotational instability (Flock et al. 2015); condensation fronts (Zhang et al. 2015); dust sintering (Okuzumi et al. 2016); photoevaporation (Ercolano et al. 2017).”