scholarly journals Evolution of porous dust grains in protoplanetary discs – I. Growing grains

2020 ◽  
Vol 493 (2) ◽  
pp. 1788-1800
Author(s):  
Anthony J L Garcia ◽  
Jean-François Gonzalez
Keyword(s):  
Numerical Simulations ◽  
Grain Growth ◽  
Planet Formation ◽  
Dust Grains ◽  
Porosity Evolution ◽  
Direct Formation ◽  
Porous Grains ◽  
Small Dust ◽  
Protoplanetary Discs

ABSTRACT One of the main problems in planet formation, hampering the growth of small dust to planetesimals, is the so-called radial-drift barrier. Pebbles of cm to dm sizes are thought to drift radially across protoplanetary discs faster than they can grow to larger sizes, and thus to be lost to the star. To overcome this barrier, drift has to be slowed down or stopped, or growth needs to be sped up. In this paper, we investigate the role of porosity on both drift and growth. We have developed a model for porosity evolution during grain growth and applied it to numerical simulations of protoplanetary discs. We find that growth is faster for porous grains, enabling them to transition to the Stokes drag regime, decouple from the gas, and survive the radial-drift barrier. Direct formation of small planetesimals from porous dust is possible over large areas of the disc.

scholarly journals Dust distribution in circumstellar shells

2011 ◽  
Vol 7 (S283) ◽  
pp. 516-517
Author(s):  
Allard-Jan van Marle ◽  
Zakaria Meliani ◽  
Rony Keppens ◽  
Leen Decin
Keyword(s):  
Numerical Simulations ◽  
Stellar Wind ◽  
Dust Grains ◽  
Gas Distribution ◽  
Strongly Coupled ◽  
Hydrodynamical Models ◽  
Weakly Coupled ◽  
Circumstellar Shells ◽  
Dust Distribution ◽  
Small Dust

AbstractWe present numerical simulations of the hydrodynamical interactions that produce circumstellar shells. These simulations include several scenarios, such as wind-wind interaction and wind-ISM collisions. In our calculations we have taken into account the presence of dust in the stellar wind. Our results show that, while small dust grains tend to be strongly coupled to the gas, large dust grains are only weakly coupled. As a result, the distribution of the large dust grains is not representative of the gas distribution. Combining these results with observations may give us a new way of validating hydrodynamical models of the circumstellar medium.

scholarly journals Characterisation of SPH noise in simulations of protoplanetary discs

2010 ◽  
Vol 6 (S276) ◽  
pp. 393-394 ◽  
Author(s):  
Serena E. Arena ◽  
Jean-François Gonzalez ◽  
Elisabeth Crespe
Keyword(s):  
Numerical Simulations ◽  
Statistical Study ◽  
Accretion Discs ◽  
Dust Grains ◽  
Complex Interplay ◽  
Protoplanetary Discs

AbstractThe effects of turbulence on the dynamics of dust grains in protoplanetary discs is of relevant importance in the study of pre-planetesimal formation. The complex interplay between gas and dust and the modelling of turbulence require numerical simulations.A statistical study of the noise in SPH simulations of gas-only protoplanetary accretion discs is performed in order to determine if it could mimic turbulence and to what extent.

scholarly journals Size and density sorting of dust grains in SPH simulations of protoplanetary discs – II. Fragmentation

2019 ◽  
Vol 490 (3) ◽  
pp. 4428-4446 ◽  
Author(s):  
F C Pignatale ◽  
J-F Gonzalez ◽  
Bernard Bourdon ◽  
Caroline Fitoussi
Keyword(s):  
Grain Growth ◽  
Time Scales ◽  
Rapid Growth ◽  
Chemical Fractionation ◽  
Combined Effects ◽  
Dust Grains ◽  
Two Phase ◽  
Growth Regime ◽  
Fragmentation Thresholds ◽  
Protoplanetary Discs

ABSTRACT Grain growth and fragmentation are important processes in building up large dust aggregates in protoplanetary discs. Using a 3D two-phase (gas–dust) sph code, we investigate the combined effects of growth and fragmentation of a multiphase dust with different fragmentation thresholds in a time-evolving disc. We find that our fiducial disc, initially in a fragmentation regime, moves towards a pure-growth regime in a few thousands years. Time-scales change as a function of the disc and dust properties. When fragmentation is efficient, it produces, in different zones of the disc, Fe/Si and rock/ice ratios different from those predicted when only pure growth is considered. Chemical fractionation and the depletion/enrichment in iron observed in some chondrites can be linked to the size–density sorting and fragmentation properties of precursor dusty grains. We suggest that aggregation of chondritic components could have occurred where/when fragmentation was not efficient if their aerodynamical sorting has to be preserved. Chondritic components would allow aerodynamical sorting in a fragmentation regime only if they have similar fragmentation properties. We find that, in the inner disc, and for the same interval of time, fragmenting dust can grow larger when compared to the size of grains predicted by pure growth. This counter-intuitive behaviour is due to the large amount of dust that piles up in a fragmenting zone followed by the rapid growth that occurs when this zone transitions to a pure growth regime. As an important consequence, dust can overcome the radial-drift barrier within a few thousands years.

scholarly journals MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure

2021 ◽  
Vol 504 (1) ◽  
pp. 280-299
Author(s):  
Marija R Jankovic ◽  
James E Owen ◽  
Subhanjoy Mohanty ◽  
Jonathan C Tan
Keyword(s):  
Energy Transport ◽  
Threshold Temperature ◽  
Mass Star ◽  
Dust Grains ◽  
Solar Mass ◽  
Detailed Model ◽  
Short Period ◽  
Pressure Maximum ◽  
Ion Emission ◽  
Protoplanetary Discs

ABSTRACT Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magnetorotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization, and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($\dot{M}\, \sim \, 10^{-8}$ M⊙ yr−1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the mid-plane. As a result, both the disc mid-plane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges on to grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.

scholarly journals Earth-size planet formation in the habitable zone of circumbinary stars

2020 ◽  
Vol 494 (1) ◽  
pp. 1045-1057 ◽  
Author(s):  
G O Barbosa ◽  
O C Winter ◽  
A Amarante ◽  
A Izidoro ◽  
R C Domingos ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Planet Formation ◽  
Terrestrial Planet ◽  
Close Binary ◽  
Habitable Zone ◽  
Density Profiles ◽  
Habitable Planets ◽  
Habitable Zones ◽  
Test Particles ◽  
The Stability

ABSTRACT This work investigates the possibility of close binary (CB) star systems having Earth-size planets within their habitable zones (HZs). First, we selected all known CB systems with confirmed planets (totaling 22 systems) to calculate the boundaries of their respective HZs. However, only eight systems had all the data necessary for the computation of HZ. Then, we numerically explored the stability within HZs for each one of the eight systems using test particles. From the results, we selected five systems that have stable regions inside HZs, namely Kepler-34,35,38,413, and 453. For these five cases of systems with stable regions in HZ, we perform a series of numerical simulations for planet formation considering discs composed of planetary embryos and planetesimals, with two distinct density profiles, in addition to the stars and host planets of each system. We found that in the case of the Kepler-34 and 453 systems, no Earth-size planet is formed within HZs. Although planets with Earth-like masses were formed in Kepler-453, they were outside HZ. In contrast, for the Kepler-35 and 38 systems, the results showed that potentially habitable planets are formed in all simulations. In the case of the Kepler-413system, in just one simulation, a terrestrial planet was formed within HZ.

scholarly journals Numerical Simulations of a Gravity Wave Event over CCOPE. Part I: The Role of Geostrophic Adjustment in Mesoscale Jetlet Formation

1997 ◽  
Vol 125 (6) ◽  
pp. 1185-1211 ◽  
Author(s):  
Michael L. Kaplan ◽  
Steven E. Koch ◽  
Yuh-Lang Lin ◽  
Ronald P. Weglarz ◽  
Robert A. Rozumalski
Keyword(s):  
Numerical Simulations ◽  
Gravity Wave ◽  
Geostrophic Adjustment ◽  
Wave Event

Microstructure of Polycrystalline MgO Penetrated by a Silicate Liquid

1996 ◽  
Vol 2 (3) ◽  
pp. 113-128 ◽  
Author(s):  
Sundar Ramamurthy ◽  
Michael P. Mallamaci ◽  
Catherine M. Zimmerman ◽  
C. Barry Carter ◽  
Peter R. Duncombe ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Glassy Phase ◽  
Silicate Liquid ◽  
Two Phase ◽  
The Matrix ◽  
Devitrification Process ◽  
Phase Mixture

Dense, polycrystalline MgO was infiltrated with monticellite (CaMgSiO4) liquid to study the penetration of liquid along the grain boundaries of MgO. Grain growth was found to be restricted with increasing amounts of liquid. The inter-granular regions were generally found to be comprised of a two-phase mixture: crystalline monticellite and a glassy phase rich in the impurities present in the starting MgO material. MgO grains act as seeding agents for the crystallization of monticellite. The location and composition of the glassy phase with respect to the MgO grains emphasizes the role of intergranular liquid during the devitrification process in “snowplowing” impurities present in the matrix.

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