scholarly journals Dust Settling and Clumping in MRI-turbulent Outer Protoplanetary Disks

2022 ◽  
Vol 924 (1) ◽  
pp. 3
Author(s):  
Ziyan Xu ◽  
Xue-Ning Bai
Keyword(s):  
Protoplanetary Disks ◽  
Rotational Instability ◽  
Local Pressure ◽  
Zonal Flows ◽  
Streaming Instability ◽  
Numerical Studies ◽  
Outer Disk ◽  
External Turbulence ◽  
Local Shearing ◽  
Modest Level

Abstract Planetesimal formation is a crucial yet poorly understood process in planet formation. It is widely believed that planetesimal formation is the outcome of dust clumping by the streaming instability (SI). However, recent analytical and numerical studies have shown that the SI can be damped or suppressed by external turbulence, and at least the outer regions of protoplanetary disks are likely weakly turbulent due to magneto-rotational instability (MRI). We conduct high-resolution local shearing-box simulations of hybrid particle-gas magnetohydrodynamics (MHD), incorporating ambipolar diffusion as the dominant nonideal MHD effect, applicable to outer disk regions. We first show that dust backreaction enhances dust settling toward the midplane by reducing turbulence correlation time. Under modest level of MRI turbulence, we find that dust clumping is in fact easier than the conventional SI case, in the sense that the threshold of solid abundance for clumping is lower. The key to dust clumping includes dust backreaction and the presence of local pressure maxima, which in our work is formed by the MRI zonal flows overcoming background pressure gradient. Overall, our results support planetesimal formation in the MRI-turbulent outer protoplanetary disks, especially in ring-like substructures.

scholarly journals Dust-driven viscous ring-instability in protoplanetary disks

2018 ◽  
Vol 609 ◽  
pp. A50 ◽  
Author(s):  
C. P. Dullemond ◽  
A. B. T. Penzlin
Keyword(s):  
Surface Density ◽  
Scattered Light ◽  
Protoplanetary Disks ◽  
Continuum Emission ◽  
Rotational Instability ◽  
Local Pressure ◽  
Ionization Degree ◽  
Local Maxima ◽  
Gas Ionization ◽  
Small Dust

Protoplanetary disks often appear as multiple concentric rings in dust continuum emission maps and scattered light images. These features are often associated with possible young planets in these disks. Many non-planetary explanations have also been suggested, including snow lines, dead zones and secular gravitational instabilities in the dust. In this paper we suggest another potential origin. The presence of copious amounts of dust tends to strongly reduce the conductivity of the gas, thereby inhibiting the magneto-rotational instability, and thus reducing the turbulence in the disk. From viscous disk theory it is known that a disk tends to increase its surface density in regions where the viscosity (i.e. turbulence) is low. Local maxima in the gas pressure tend to attract dust through radial drift, increasing the dust content even more. We have investigated mathematically if this could potentially lead to a feedback loop in which a perturbation in the dust surface density could perturb the gas surface density, leading to increased dust drift and thus amplification of the dust perturbation and, as a consequence, the gas perturbation. We find that this is indeed possible, even for moderately small dust grain sizes, which drift less efficiently, but which are more likely to affect the gas ionization degree. We speculate that this instability could be triggered by the small dust population initially, and when the local pressure maxima are strong enough, the larger dust grains get trapped and lead to the familiar ring-like shapes. We also discuss the many uncertainties and limitations of this model.

scholarly journals Planetesimal Formation in Zonal Flows Arising in Magneto-Rotationally-Unstable Protoplanetary Disks

2012 ◽  
Vol 8 (S293) ◽  
pp. 244-249
Author(s):  
Karsten Dittrich ◽  
Hubert Klahr ◽  
Anders Johansen
Keyword(s):  
Protoplanetary Disks ◽  
Life Time ◽  
Zonal Flow ◽  
Turbulent Medium ◽  
Dust Particles ◽  
Zonal Flows ◽  
Flow Features ◽  
Pressure Scale ◽  
First Time ◽  
Local Shearing

AbstractRecent simulations show long -lived sub- and super-Keplerian flows in protoplanetary disks. These so-called zonal flows are found in local as well as global simulations of magneto-rotationally unstable disks. We investigate the strength and life-time of the resulting long-lived gas over- and under-densities as well as particle concentrations function of the azimuthal and radial size of the local shearing box. Changes in the azimuthal extent do not affect the zonal flow features. However, strength and life-time of zonal flows increase with increasing radial box sizes. Our simulations show indications, and support earlier results, that zonal flows have a natural length scale of approximately 5 pressure scale heights. For the first time, the reaction of dust particles in boxes with zonal flows are studied. We show that particles of some centimeters in size reach a hundred-fold higher density than initially, without any self-gravitating forces acting on the point masses. We further investigate collision velocities of dust grains in a turbulent medium.

scholarly journals Self-Sustaining Vortices in Protoplanetary Disks: Setting the Stage for Planetary System Formation

2020 ◽  
Author(s):  
Zsolt Regály ◽  
Kundan Kadam ◽  
Cornelis Dullemond
Keyword(s):  
Planetary System ◽  
Protoplanetary Disks ◽  
Dust Particles ◽  
Rotational Instability ◽  
Small Scale ◽  
Hydrodynamic Simulations ◽  
System Formation ◽  
Streaming Instability ◽  
Growth Barriers ◽  
Core Accretion

Abstract The core accretion scenario of planet formation assumes that planetesimals and planetary embryos are formed during the primordial, gaseous phases of the protoplanetary disk. However, how the dust particles overcome the traditional growth barriers is not well understood. Recently proposed viscous ring-instability explains the concentric rings observed in protoplanetary disks by assuming that the dust grains can reduce the gas conductivity, which can weaken the magneto-rotational instability. We present an analysis of this model with the help of GPU-based numerical hydrodynamic simulations of coupled gas and dust in the thin-disk limit. During the evolution of the disk the dusty rings become Rossby unstable and break up into a cascade of small-scale vortices. The vortices form secularly stable dusty structures, where the rapid dust growth can occur via the streaming instability. The phenomenon of self-sustaining vortices is consistent with observational constraints of exoplanets and sets a favorable environment for planetary system formation.

scholarly journals A Lagrangian model for dust evolution in protoplanetary disks: formation of wet and dry planetesimals at different stellar masses

2018 ◽  
Vol 620 ◽  
pp. A134 ◽  
Author(s):  
Djoeke Schoonenberg ◽  
Chris W. Ormel ◽  
Sebastiaan Krijt
Keyword(s):  
Accretion Rate ◽  
Protoplanetary Disks ◽  
Particle Method ◽  
Solid Particles ◽  
Lagrangian Model ◽  
Low Mass Stars ◽  
Streaming Instability ◽  
Mass Fluxes ◽  
Gas Accretion ◽  
Stellar Masses

We introduce a new Lagrangian smooth-particle method to model the growth and drift of pebbles in protoplanetary disks. The Lagrangian nature of the model makes it especially suited to following characteristics of individual (groups of) particles, such as their composition. In this work we focus on the water content of solid particles. Planetesimal formation via streaming instability is taken into account, partly based on previous results on streaming instability outside the water snowline that were presented in a recent publication. We validated our model by reproducing earlier results from the literature and apply our model to steady-state viscous gas disks (with constant gas accretion rate) around stars with different masses. We also present various other models where we explore the effects of pebble accretion, the fragmentation velocity threshold, the global metallicity of the disk, and a time-dependent gas accretion rate. We find that planetesimals preferentially form in a local annulus outside the water snowline, at early times in the lifetime of the disk (≲105 yr), when the pebble mass fluxes are high enough to trigger the streaming instability. During this first phase in the planet formation process, the snowline location hardly changes due to slow viscous evolution, and we conclude that assuming a constant gas accretion rate is justified in this first stage. The efficiency of converting the solids reservoir of the disk to planetesimals depends on the location of the water snowline. Cooler disks with a closer-in water snowline are more efficient at producing planetesimals than hotter disks where the water snowline is located further away from the star. Therefore, low-mass stars tend to form planetesimals more efficiently, but any correlation may be overshadowed by the spread in disk properties.

scholarly journals Streaming instability of multiple particle species in protoplanetary disks

2018 ◽  
Vol 618 ◽  
pp. A75 ◽  
Author(s):  
Noemi Schaffer ◽  
Chao-Chin Yang ◽  
Anders Johansen
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Protoplanetary Disks ◽  
Single Species ◽  
Stokes Number ◽  
Dust Particles ◽  
Particle Sizes ◽  
Particle Species ◽  
Streaming Instability ◽  
Large Particles

The radial drift and diffusion of dust particles in protoplanetary disks affect both the opacity and temperature of such disks, as well as the location and timing of planetesimal formation. In this paper, we present results of numerical simulations of particle-gas dynamics in protoplanetary disks that include dust grains with various size distributions. We have considered three scenarios in terms of particle size ranges, one where the Stokes number τs = 10−1−100, one where τs = 10−4−10−1, and finally one where τs = 10−3−100. Moreover, we considered both discrete and continuous distributions in particle size. In accordance with previous works we find in our multispecies simulations that different particle sizes interact via the gas and as a result their dynamics changes compared to the single-species case. The larger species trigger the streaming instability and create turbulence that drives the diffusion of the solid materials. We measured the radial equilibrium velocity of the system and find that the radial drift velocity of the large particles is reduced in the multispecies simulations and that the small particle species move on average outwards. We also varied the steepness of the size distribution, such that the exponent of the solid number density distribution, dN∕da ∝ a−q, is either q = 3 or q = 4. Overall, we find that the steepness of the size distribution and the discrete versus continuous approach have little impact on the results. The level of diffusion and drift rates are mainly dictated by the range of particle sizes. We measured the scale height of the particles and observe that small grains are stirred up well above the sedimented midplane layer where the large particles reside. Our measured diffusion and drift parameters can be used in coagulation models for planet formation as well as to understand relative mixing of the components of primitive meteorites (matrix, chondrules and CAIs) prior to inclusion in their parent bodies.

Effect of Corrugation on the Performance of Porous Baffles Used as Weather Shelters on Oil and Gas Platforms

2014 ◽  
Author(s):  
Geanette Polanco ◽  
Mohamad Y. Mustafa ◽  
Yizhong Xu
Keyword(s):  
Experimental Data ◽  
Oil And Gas ◽  
Flow Characteristics ◽  
Local Pressure ◽  
Numerical Studies ◽  
Dimensional Simulation ◽  
Stream Lines ◽  
Offshore Oil ◽  
Sheltered Area ◽  
Good Agreement

Porous baffles are usually used for weather protection on onshore and offshore oil installations in order to provide a sheltered area for personnel to operate. Corrugated fences are more favourable than flat fences in large installations, due to their increased stiffness; however, the performance of those fences is expected to differ from flat fences due to changes in porosity and flow structure. In this work, the experimental and numerical studies of the influence of corrugated fence on the flow characteristics are presented. The tri-dimensional effect imposed by the angle of corrugation and the depth of the fence influences the windward and leeward flow characteristics with respect to the fence. Velocity coefficient is used as one important parameter for measuring the performance of porous fences. It was found that, under similar conditions, the total obstruction produced by the corrugated fence varies significantly from that of the flat fence. Hence, velocity reduction for a corrugated fence system is expected to be smaller. A complete description of the physics of the fluid mechanics around the fence is given. Furthermore, the behaviour of the stream lines close to the fences in both cases; corrugated and non-corrugated, were studied using CFD techniques. Through observation of local pressure distribution, it was possible to reveal how velocity variations were concentrated around the inclined sections of the corrugated fence. In performing the numerical simulations, a two dimensional approach was initially implemented to capture the flow behaviour in the vicinity of the inclined sections. Subsequently, a tri-dimensional simulation on a section of the fence was undertaken and compared with experimental data. The results of the simulations were in good agreement with experimental data obtained from wind tunnel tests.

scholarly journals Carbon depletion observed inside T Tauri inner rims

2019 ◽  
Vol 632 ◽  
pp. A32 ◽  
Author(s):  
M. K. McClure
Keyword(s):  
Carbon Content ◽  
Near Infrared ◽  
Protoplanetary Disks ◽  
Far Infrared ◽  
T Tauri Stars ◽  
Outer Disk ◽  
Carbon Abundance ◽  
T Tauri ◽  
Medium Resolution ◽  
Complete Set

Context. The carbon content of protoplanetary disks is an important parameter to characterize planets formed at different disk radii. There is some evidence from far-infrared and submillimeter observations that gas in the outer disk is depleted in carbon, with a corresponding enhancement of carbon-rich ices at the disk midplane. Observations of the carbon content inside of the inner sublimation rim could confirm how much carbon remains locked in kilometer size bodies in the disk. Aims. I aim to determine the density, temperature, and carbon abundance inside the disk dust sublimation rim in a set of T Tauri stars with full protoplanetary disks. Methods. Using medium-resolution, near-infrared (0.8–2.5 μm) spectra and the new Gaia DR2 distances, I self-consistently determine the stellar, extinction, veiling, and accretion properties of the 26 stars in my sample. From these values, and non-accreting T Tauri spectral templates, I extract the inner disk excess of the target stars from their observed spectra. Then I identify a series of C0 recombination lines in 18 of these disks and use the CHIANTI atomic line database with an optically thin slab model to constrain the average ne, Te, and nc for these lines in the five disks with a complete set of lines. By comparing these values with other slab models of the inner disk using the Cloudy photoionization code, I also constrain nH and the carbon abundance, XC, and hence the amount of carbon “missing” from the slab. For one disk, DR Tau, I use relative abundances for the accretion stream from the literature to also determine XSi and XN. Results. The inner disks modeled here are extremely dense (nH ~ 1016 cm−3), warm (Te ~ 4500 K), and moderately ionized (log Xe ~ 3.3). Three of the five modeled disks show robust carbon depletion up to a factor of 42 relative to the solar value. I discuss multiple ways in which the “missing” carbon could be locked out of the accreting gas. Given the high-density inner disk gas, evidence for radial drift, and lack of obvious gaps in these three systems, their carbon depletion is most consistent with the “missing” carbon being sequestered in kilometer size bodies. For DR Tau, nitrogen and silicon are also depleted by factors of 45 and 4, respectively, suggesting that the kilometer size bodies into which the grains are locked were formed beyond the N2 snowline. I explore briefly what improvements in the models and observations are needed to better address this topic in the future.

scholarly journals Organic molecules in the protoplanetary disk of DG Tauri revealed by ALMA

2019 ◽  
Vol 623 ◽  
pp. L6 ◽  
Author(s):  
L. Podio ◽  
F. Bacciotti ◽  
D. Fedele ◽  
C. Favre ◽  
C. Codella ◽  
...  
Keyword(s):  
Column Density ◽  
Protoplanetary Disks ◽  
Temperature Inversion ◽  
Abundance Ratio ◽  
Chemical Compositions ◽  
Outer Disk ◽  
T Tauri ◽  
Dust Distribution ◽  
Disk Height ◽  
Co Emission

Context. Planets form in protoplanetary disks and inherit their chemical compositions. Aims. It is thus crucial to map the distribution and investigate the formation of simple organics, such as formaldehyde and methanol, in protoplanetary disks. Methods. We analyze ALMA observations of the nearby disk-jet system around the T Tauri star DG Tau in the o − H2CO 31, 2 − 21, 1 and CH3OH 3−2, 2 − 4−1, 4 E, 50, 5 − 40, 4 A transitions at an unprecedented resolution of $ {\sim}0{{\overset{\prime\prime}{.}}}{15} $, i.e., ∼18 au at a distance of 121 pc. Results. The H2CO emission originates from a rotating ring extending from ∼40 au with a peak at ∼62 au, i.e., at the edge of the 1.3 mm dust continuum. CH3OH emission is not detected down to an rms of 3 mJy beam−1 in the 0.162 km s−1 channel. Assuming an ortho-to-para ratio of 1.8−2.8 the ring- and disk-height-averaged H2CO column density is ∼0.3−4 × 1014 cm−2, while that of CH3OH is < 0.04−0.7 × 1014 cm−2. In the inner 40 au no o − H2CO emission is detected with an upper limit on its beam-averaged column density of ∼0.5−6 × 1013 cm−2. Conclusions. The H2CO ring in the disk of DG Tau is located beyond the CO iceline (RCO ∼ 30 au). This suggests that the H2CO abundance is enhanced in the outer disk due to formation on grain surfaces by the hydrogenation of CO ice. The emission peak at the edge of the mm dust continuum may be due to enhanced desorption of H2CO in the gas phase caused by increased UV penetration and/or temperature inversion. The CH3OH/H2CO abundance ratio is < 1, in agreement with disk chemistry models. The inner edge of the H2CO ring coincides with the radius where the polarization of the dust continuum changes orientation, hinting at a tight link between the H2CO chemistry and the dust properties in the outer disk and at the possible presence of substructures in the dust distribution.

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