scholarly journals Gas versus dust sizes of protoplanetary discs: effects of dust evolution

2019 ◽  
Vol 629 ◽  
pp. A79 ◽  
Author(s):  
L. Trapman ◽  
S. Facchini ◽  
M. R. Hogerheijde ◽  
E. F. van Dishoeck ◽  
S. Bruderer
Keyword(s):  
Grain Growth ◽  
Optical Depth ◽  
Outer Radius ◽  
Size Difference ◽  
Clear Sign ◽  
Thermochemical Model ◽  
High Fraction ◽  
Space Dust ◽  
Dust Evolution ◽  
Protoplanetary Discs

Context. The extent of the gas in protoplanetary discs is observed to be universally larger than the extent of the dust. This is often attributed to radial drift and grain growth of the millimetre grains, but line optical depth produces a similar observational signature. Aims. We investigate in which parts of the disc structure parameter space dust evolution and line optical depth are the dominant drivers of the observed gas and dust size difference. Methods. Using the thermochemical model DALI with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size dichotomy. Results. The relation between Rdust and dust evolution is non-monotonic and depends on the disc structure. The quantity Rgas is directly related to the radius where the CO column density drops below 1015 cm−2 and CO becomes photodissociated; Rgas is not affected by dust evolution but scales with the total CO content of the disc. While these cases are rare in current observations, Rgas/Rdust > 4 is a clear sign of dust evolution and radial drift in discs. For discs with a smaller Rgas/Rdust, identifying dust evolution from Rgas/Rdust requires modelling the disc structure including the total CO content. To minimize the uncertainties due to observational factors requires FWHMbeam < 1× the characteristic radius and a peak S/N > 10 on the 12CO emission moment zero map. For the dust outer radius to enclose most of the disc mass, it should be defined using a high fraction (90–95%) of the total flux. For the gas, any radius enclosing >60% of the 12CO flux contains most of the disc mass. Conclusions. To distinguish radial drift and grain growth from line optical depth effects based on size ratios requires discs to be observed at high enough angular resolution and the disc structure should to be modelled to account for the total CO content of the disc.

scholarly journals Constraining the radial drift of millimeter-sized grains in the protoplanetary disks in Lupus

2020 ◽  
Vol 638 ◽  
pp. A38 ◽  
Author(s):  
L. Trapman ◽  
M. Ansdell ◽  
M. R. Hogerheijde ◽  
S. Facchini ◽  
C. F. Manara ◽  
...  
Keyword(s):  
Grain Growth ◽  
Optical Depth ◽  
Thermal Emission ◽  
Signal To Noise Ratio ◽  
Protoplanetary Disks ◽  
Outer Radius ◽  
Size Difference ◽  
Star Forming ◽  
Dust Evolution ◽  
Depth Effects

Context. Recent ALMA surveys of protoplanetary disks have shown that for most disks the extent of the gas emission is greater than the extent of the thermal emission of millimeter-sized dust. Both line optical depth and the combined effect of radially dependent grain growth and radial drift may contribute to this observed effect. To determine whether or not radial drift is common across the disk population, quantitative estimates of the effect of line optical depth are required. Aims. For a sample of ten disks from the Lupus survey we investigate how well dust-based models without radial dust evolution reproduce the observed 12CO outer radius, and determine whether radial dust evolution is required to match the observed gas–dust size difference. Methods. Based on surface density profiles derived from continuum observations we used the thermochemical code DALI to obtain 12CO synthetic emission maps. Gas and dust outer radii of the models were calculated using the same methods as applied to the observations. The gas and dust outer radii (RCO, Rmm) calculated using only line optical depth were compared to observations on a source-by-source basis. Results. For five disks, we find RCO, obs∕Rmm, obs > RCO, mdl∕Rmm, mdl. For these disks we need both dust evolution and optical depth effects to explain the observed gas–dust size difference. For the other five disks, the observed RCO∕Rmm lies within the uncertainties on RCO, mdl∕Rmm, mdl due to noise. For these disks the observed gas–dust size difference can be explained using only line optical depth effects. We also identify six disks not included in our initial sample but part of a survey of the same star-forming region that show significant signal-to-noise ratio (S∕N ≥ 3) 12CO J = 2−1 emission beyond 4 × Rmm. These disks, for which no RCO is available, likely have RCO∕Rmm ≫ 4 and are difficult to explain without substantial dust evolution. Conclusions. Most of the disks in our sample of predominantly bright disks are consistent with radial drift and grain growth. We also find six faint disks where the observed gas–dust size difference hints at considerable radial drift and grain growth, suggesting that these are common features among both bright and faint disks. The effects of radial drift and grain growth can be observed in disks where the dust and gas radii are significantly different, while more detailed models and deeper observations are needed to see this effect in disks with smaller differences.

scholarly journals Rapid grain growth in post-AGB disc systems from far-infrared and sub-millimetre photometry

2020 ◽  
Vol 494 (2) ◽  
pp. 2925-2936
Author(s):  
P Scicluna ◽  
F Kemper ◽  
A Trejo ◽  
J P Marshall ◽  
S Ertel ◽  
...  
Keyword(s):  
Grain Growth ◽  
Time Scales ◽  
Far Infrared ◽  
Asymptotic Giant Branch ◽  
Growth Time ◽  
Agb Stars ◽  
Keplerian Orbits ◽  
Dust Evolution ◽  
Astronomical Dust ◽  
Protoplanetary Discs

ABSTRACT The time-scales on which astronomical dust grows remain poorly understood, with important consequences for our understanding of processes like circumstellar disc evolution and planet formation. A number of post-asymptotic giant branch (AGB) stars are found to host optically thick, dust- and gas-rich circumstellar discs in Keplerian orbits. These discs exhibit evidence of dust evolution, similar to protoplanetary discs; however, since post-AGB discs have substantially shorter lifetimes than protoplanetary discs, they may provide new insights on the grain-growth process. We examine a sample of post-AGB stars with discs to determine the far-infrared and sub-millimetre spectral index by homogeneously fitting a sample of data from Herschel, the Submillimeter Array (SMA), and the literature. We find that grain growth to at least hundreds of micrometres is ubiquitous in these systems, and that the distribution of spectral indices is more similar to that of protoplanetary discs than debris discs. No correlation is found with the mid-infrared colours of the discs, implying that grain growth occurs independently of the disc structure in post-AGB discs. We infer that grain growth to ∼millimetre sizes must occur on time-scales &lt;&lt;105 yr, perhaps by orders of magnitude, as the lifetimes of these discs are expected to be ≲105 yr and all objects have converged to the same state. This growth time-scale is short compared to the results of models for protoplanetary discs including fragmentation and may provide new constraints on the physics of grain growth.

scholarly journals Influence of grain growth on the thermal structure of protoplanetary discs

2020 ◽  
Vol 640 ◽  
pp. A63 ◽  
Author(s):  
Sofia Savvidou ◽  
Bertram Bitsch ◽  
Michiel Lambrechts
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Grain Growth ◽  
Thermal Structure ◽  
Size Composition ◽  
Size Distributions ◽  
Migration Rates ◽  
Grain Size Distributions ◽  
Hydrodynamical Simulations ◽  
Protoplanetary Discs

The thermal structure of a protoplanetary disc is regulated by the opacity that dust grains provide. However, previous works have often considered simplified prescriptions for the dust opacity in hydrodynamical disc simulations, for example, by considering only a single particle size. In the present work, we perform 2D hydrodynamical simulations of protoplanetary discs where the opacity is self-consistently calculated for the dust population, taking into account the particle size, composition, and abundance. We first compared simulations utilizing single grain sizes to two different multi-grain size distributions at different levels of turbulence strengths, parameterized through the α-viscosity, and different gas surface densities. Assuming a single dust size leads to inaccurate calculations of the thermal structure of discs, because the grain size dominating the opacity increases with orbital radius. Overall the two grain size distributions, one limited by fragmentation only and the other determined from a more complete fragmentation-coagulation equilibrium, give comparable results for the thermal structure. We find that both grain size distributions give less steep opacity gradients that result in less steep aspect ratio gradients, in comparison to discs with only micrometer-sized dust. Moreover, in the discs with a grain size distribution, the innermost (<5 AU) outward migration region is removed and planets embedded in such discs experience lower migration rates. We also investigated the dependency of the water iceline position on the alpha-viscosity (α), the initial gas surface density (Σg,0) at 1 AU and the dust-to-gas ratio (fDG) and find rice ∝ α0.61Σg,00.8fDG0.37 independently of the distribution used in the disc. The inclusion of the feedback loop between grain growth, opacities, and disc thermodynamics allows for more self-consistent simulations of accretion discs and planet formation.

scholarly journals The ‘Isothermal’ Phase of Nova Dust Shells

1983 ◽  
Vol 72 ◽  
pp. 133-138
Author(s):  
R.M. Mitchel ◽  
A. Evans ◽  
M.F. Bode
Keyword(s):  
Grain Size ◽  
Temperature Gradient ◽  
Infrared Spectrum ◽  
Grain Growth ◽  
Optical Depth ◽  
Effective Temperature ◽  
Near Infrared ◽  
Dust Shell ◽  
Consistent Picture ◽  
Significant Temperature

AbstractWe describe a model for the evolution of the infrared spectrum of the dust shell of nova NQ Vul. The effects of nucleation and grain growth, together with.extended, but diminishing, mass loss from the nova, are included. The variations in the effective temperature of the dust shell that occur near infrared maximum may be understood in terms of varying optical depth in a dust shell having significant temperature gradient. However, a more consistent picture is shown to combine interrelated optical depth and grain size variations.

scholarly journals The efficiency of grain growth in the diffuse interstellar medium

2021 ◽  
Vol 502 (2) ◽  
pp. 2438-2445
Author(s):  
F D Priestley ◽  
I De Looze ◽  
M J Barlow
Keyword(s):  
Interstellar Medium ◽  
Size Distribution ◽  
Gas Phase ◽  
Grain Growth ◽  
Common Assumption ◽  
Small Grains ◽  
Far Ultraviolet ◽  
Dust Evolution ◽  
Charged Ions ◽  
Positively Charged

ABSTRACT Grain growth by accretion of gas-phase metals is a common assumption in models of dust evolution, but in dense gas, where the time-scale is short enough for accretion to be effective, material is accreted in the form of ice mantles rather than adding to the refractory grain mass. It has been suggested that negatively charged small grains in the diffuse interstellar medium (ISM) can accrete efficiently due to the Coulomb attraction of positively-charged ions, avoiding this issue. We show that this inevitably results in the growth of the small-grain radii until they become positively charged, at which point further growth is effectively halted. The resulting gas-phase depletions under diffuse ISM conditions are significantly overestimated when a constant grain size distribution is assumed. While observed depletions can be reproduced by changing the initial size distribution or assuming highly efficient grain shattering, both options result in unrealistic levels of far-ultraviolet extinction. We suggest that the observed elemental depletions in the diffuse ISM are better explained by higher initial depletions, combined with inefficient dust destruction by supernovae at moderate ($n_{\rm H}\sim 30 \, {\rm cm}^{-3}$) densities, rather than by higher accretion efficiences.

Control of Grain Boundary Microstructures in Sputtered Gold Thin Films by Surface Energy-Driven Grain Growth

2012 ◽  
Vol 706-709 ◽  
pp. 2880-2885 ◽  
Author(s):  
Shigeaki Kobayashi ◽  
Ryouta Fukasawa ◽  
Tadao Watanabe
Keyword(s):  
Thin Films ◽  
Surface Energy ◽  
Grain Boundary ◽  
Grain Growth ◽  
High Performance ◽  
Coincidence Site Lattice ◽  
Grain Boundary Engineering ◽  
High Fraction ◽  
Percolation Phenomena ◽  
Gold Thin Films

The evolution of grain boundary microstructures in gold thin films during annealing was investigated in order to find a clue to the development of high performance thin films by grain boundary engineering. The {111} oriented grains with the lowest surface energy were preferentially grown by surface energy-driven grain growth during annealing. The sharp {111} texture was developed by annealing at the temperature more than 873K. The remarkably high fraction of low-Σ coincidence site lattice (CSL) boundaries occurred when the area fraction of {111} texture increased to more than 95%. In particular, the fraction of some low-Σ CSL boundaries (Σ1,Σ3,Σ7) for the most sharply {111} textured specimen was found to be one order higher than those predicted for a random polycrystal. The utility of grain boundary engineering is discussed for controlling the performance degradation caused by the percolation phenomena of grain boundary diffusion in gold thin films.

scholarly journals Observable signatures of dust evolution mechanisms which shape the planet forming regions

2010 ◽  
Vol 6 (S276) ◽  
pp. 450-452
Author(s):  
Olja Panić ◽  
Tilman Birnstiel ◽  
Ruud Visser ◽  
Elco van Kampen
Keyword(s):  
Grain Growth ◽  
Radial Distribution ◽  
State Of The Art ◽  
Gas Evolution ◽  
Viscous Gas ◽  
Dust Evolution

AbstractOverdensity of dust with respect to the gas in the planet forming regions is a crucial prerequisite to form larger bodies and eventually planets. We use a state-of-the-art code to simulate dust evolution processes in gas-rich circumstellar discs, including the viscous gas evolution. We find significant deviations of the radial distribution of dust from that of the gas as early as 1-2Myr. These deviations are closely related to the efficiency of grain growth. Apparent discrepancies between dust and gas distributions are suggested by the current millimetre interferometer observations, and ALMA will allow us tointerpret any such discrepancies in the context of dust evolution.

Dust evolution in galaxies at z > 7

2019 ◽  
Vol 15 (S341) ◽  
pp. 312-313
Author(s):  
Tsutomu T. Takeuchi ◽  
Ryosuke S. Asano ◽  
Sayaka Nagasaki ◽  
Takaya Nozawa ◽  
Yoichi Tamura ◽  
...  
Keyword(s):  
Grain Growth ◽  
Stellar Mass ◽  
Dust Production ◽  
Huge Amount ◽  
Dust Mass ◽  
Dust Destruction ◽  
Dust Grain ◽  
Dust Evolution ◽  
Dust Grain Growth ◽  
The Universe

AbstractRecently huge amount of dust Mdust ≃ 106−7M⊙ in galaxies at z = 7–8 has been discovered by ALMA observations. The suggested timescale of the dust production was a few–several×108 yr, while the stellar mass was several × 109M⊙. This amount of dust cannot be easily explained only by a supply from supernovae if we consider the dust destruction by reverse shocks. We propose that these values can be consistently explained if we take into account the grain growth in the interstellar medium (ISM). This scenario successfully reproduces the evolution of the dust mass, as well as the SFR, and stellar mass simultaneously. We conclude that even at such an early epoch of the Universe, the dust grain growth in the ISM plays a significant role in galaxies.

scholarly journals Self-induced dust traps around snow lines in protoplanetary discs

2019 ◽  
Vol 492 (1) ◽  
pp. 210-222 ◽  
Author(s):  
Arnaud Vericel ◽  
Jean-François Gonzalez
Keyword(s):  
Carbon Monoxide ◽  
The Self ◽  
Dust Particles ◽  
Parameter Study ◽  
Volatile Species ◽  
Dust Trap ◽  
Multiple Observations ◽  
Snow Line ◽  
Dust Evolution ◽  
Protoplanetary Discs

ABSTRACT Dust particles need to grow efficiently from micrometre sizes to thousands of kilometres to form planets. With the growth of millimetre to metre sizes being hindered by a number of barriers, the recent discovery that dust evolution is able to create ‘self-induced’ dust traps shows promises. The condensation and sublimation of volatile species at certain locations, called snow lines, are also thought to be important parts of planet formation scenarios. Given that dust sticking properties change across a snow line, this raises the question: how do snow lines affect the self-induced dust trap formation mechanism? The question is particularly relevant with the multiple observations of the carbon monoxide (CO) snow line in protoplanetary discs, since its effect on dust growth and dynamics is yet to be understood. In this paper, we present the effects of snow lines in general on the formation of self-induced dust traps in a parameter study, and then focus on the CO snow line. We find that for a range of parameters, a dust trap forms at the snow line where the dust accumulates and slowly grows, as found for the water snow line in a previous work. We also find that, depending on the grains’ sticking properties on either side of the CO snow line, it could be either a starting or braking point for dust growth and drift. This could provide clues to understand the link between dust distributions and snow lines in protoplanetary disc observations.

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