Recycling of Planetary Proto-Atmospheres

2020 ◽  
Author(s):  
Tobias Moldenhauer ◽  
Rolf Kuiper ◽  
Wilhelm Kley ◽  
Chris Ormel
Keyword(s):  
Critical Mass ◽  
Three Dimensional ◽  
Planetary Atmosphere ◽  
Radiation Hydrodynamics ◽  
Quasi Steady State ◽  
Local Frame ◽  
Tracer Particles ◽  
Quantitative Manner ◽  
Gas Accretion ◽  
Core Accretion

<p>Protoplanets formed by core accretion can become massive enough to accrete gas from the disk they are born in. If the<br />planetary proto-atmosphere exceeds a critical mass, runaway gas accretion starts and the planetary atmosphere collapses into a gas<br />giant. In recent years, many close-in super-Earths have been observed which raises the question on how they avoided becoming hot<br />Jupiters. We investigate the recycling hypothesis as a possible mechanism to avoid the collapse of the atmosphere.<br />We use three-dimensional radiation-hydrodynamics to simulate the formation of proto-atmosphere in the local frame around<br />the planet. In post-processing we use tracer particles to calculate the shape of the atmosphere and determine the non-uniform recycling<br />timescale in a quantitative manner. Our simulations converge to a quasi-steady state where the velocity field of the gas does not change anymore. For the<br />parameter space explored, a = 0.1 au, m_c ∈ [1, 2, 5, 10] M_Earth, we find that recycling of the atmosphere counteracts the collapse by<br />preventing the gas from cooling efficiently.</p>

scholarly journals Structure and instability of the ionization fronts around moving black holes

2020 ◽  
Vol 495 (3) ◽  
pp. 2966-2978 ◽  
Author(s):  
Kazuyuki Sugimura ◽  
Massimo Ricotti
Keyword(s):  
Black Holes ◽  
Three Dimensional ◽  
Critical Value ◽  
Radiation Hydrodynamics ◽  
X Rays ◽  
Physical Processes ◽  
X Ray ◽  
Ionization Fronts ◽  
Similar Restriction ◽  
Gas Accretion

ABSTRACT In this paper, we focus on understanding the physical processes that lead to stable or unstable ionization fronts (I-fronts) observed in simulations of moving black holes (BHs). The front instability may trigger bursts of gas accretion, rendering the BH significantly more luminous than at steady state. We perform a series of idealized three-dimensional radiation hydrodynamics simulations resolving the I-fronts around BHs of mass MBH and velocity $v$∞ accreting from a medium of density nH. The I-front, with radius RI, transitions from D-type to R-type as the BH velocity becomes larger than a critical value $v_\mathrm{R}\sim 40\, \mathrm{km\,s}^{-1}$. The D-type front is preceded by a bow-shock of thickness ΔRI that decreases as $v$∞ approaches $v$R. We find that both D-type and R-type fronts can be unstable given the following two conditions: (i) for D-type fronts the shell thickness must be ΔRI/RI < 0.05 (i.e. $v_\infty \gtrsim 20\, \mathrm{km\,s}^{ -1}$), while no similar restriction holds for R-type fronts; (ii) the temperature jump across the I-front must be TII/TI > 3. This second condition is satisfied if $T_\mathrm{I}\lt 5000\, \mathrm{K}$ or if $n_\mathrm{H}\, M_\mathrm{BH} \gtrsim 10^6\, M_\odot \, \mathrm{cm^{-3}}$. Due to X-ray pre-heating typically $T_\mathrm{I} \sim 10^4\, \mathrm{K}$, unless the D-type shell is optically thick to X-rays, which also happens when $n_\mathrm{H}\, M_\mathrm{BH}$ is greater than a metallicity-dependent critical value. We thus conclude that I-fronts around BHs are unstable only for relatively massive BHs moving trough very dense molecular clouds. We briefly discuss the observational consequences of the X-ray luminosity bursts likely associated with this instability.

scholarly journals HERACLES: a three-dimensional radiation hydrodynamics code

2007 ◽  
Vol 464 (2) ◽  
pp. 429-435 ◽  
Author(s):  
M. González ◽  
E. Audit ◽  
P. Huynh
Keyword(s):  
Three Dimensional ◽  
Radiation Hydrodynamics

scholarly journals Drops bouncing off macro-textured superhydrophobic surfaces

2017 ◽  
Vol 824 ◽  
pp. 866-885 ◽  
Author(s):  
Ali Mazloomi Moqaddam ◽  
Shyam S. Chikatamarla ◽  
Iliya V. Karlin
Keyword(s):  
Contact Time ◽  
Numerical Study ◽  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Nonlinear Behaviour ◽  
Textured Surfaces ◽  
Texture Density ◽  
Wide Range ◽  
Quantitative Manner ◽  
The Impact

Recent experiments with droplets impacting macro-textured superhydrophobic surfaces revealed new regimes of bouncing with a remarkable reduction of the contact time. Here we present a comprehensive numerical study that reveals the physics behind these new bouncing regimes and quantifies the roles played by various external and internal forces. For the first time, accurate three-dimensional simulations involving realistic macro-textured surfaces are performed. After demonstrating that simulations reproduce experiments in a quantitative manner, the study is focused on analysing the flow situations beyond current experiments. We show that the experimentally observed reduction of contact time extends to higher Weber numbers, and analyse the role played by the texture density. Moreover, we report a nonlinear behaviour of the contact time with the increase of the Weber number for imperfectly coated textures, and study the impact on tilted surfaces in a wide range of Weber numbers. Finally, we present novel energy analysis techniques that elaborate and quantify the interplay between the kinetic and surface energy, and the role played by the dissipation for various Weber numbers.

scholarly journals Metallicity effect and planet mass function in pebble-based planet formation models

2018 ◽  
Vol 619 ◽  
pp. A174 ◽  
Author(s):  
N. Brügger ◽  
Y. Alibert ◽  
S. Ataiee ◽  
W. Benz
Keyword(s):  
Internal Structure ◽  
Planet Formation ◽  
Large Fraction ◽  
Mass Function ◽  
Planetary Atmosphere ◽  
Population Synthesis ◽  
Core Accretion ◽  
Mass Functions ◽  
Synthesis Approach ◽  
Gaseous Envelope

Context. One of the main scenarios of planet formation is the core accretion model where a massive core forms first and then accretes a gaseous envelope. This core forms by accreting solids, either planetesimals or pebbles. A key constraint in this model is that the accretion of gas must proceed before the dissipation of the gas disc. Classical planetesimal accretion scenarios predict that the time needed to form a giant planet’s core is much longer than the time needed to dissipate the disc. This difficulty led to the development of another accretion scenario, in which cores grow by accretion of pebbles, which are much smaller and thus more easily accreted, leading to more rapid formation. Aims. The aim of this paper is to compare our updated pebble-based planet formation model with observations, in particular the well-studied metallicity effect. Methods. We adopt the Bitsch et al. (2015a, A&A, 575, A28) disc model and the Bitsch et al. (2015b, A&A, 582, A112) pebble model and use a population synthesis approach to compare the formed planets with observations. Results. We find that keeping the same parameters as in Bitsch et al. (2015b, A&A, 582, A112) leads to no planet growth due to a computation mistake in the pebble flux (2018b). Indeed a large fraction of the heavy elements should be put into pebbles (Zpeb∕Ztot = 0.9) in order to form massive planets using this approach. The resulting mass functions show a huge amount of giants and a lack of Neptune-mass planets, which are abundant according to observations. To overcome this issue we include the computation of the internal structure for the planetary atmosphere in our model. This leads to the formation of Neptune-mass planets but no observable giants. Furthermore, reducing the opacity of the planetary envelope more closely matches observations. Conclusions. We conclude that modelling the internal structure for the planetary atmosphere is necessary to reproduce observations.

scholarly journals The age–chemical abundance structure of the Galaxy I: evidence for a late-accretion event in the outer disc at z ∼ 0.6

2020 ◽  
Vol 494 (2) ◽  
pp. 2561-2575 ◽  
Author(s):  
Jianhui Lian ◽  
Daniel Thomas ◽  
Claudia Maraston ◽  
Olga Zamora ◽  
Jamie Tayar ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Dimensional Space ◽  
Large Fraction ◽  
Three Dimensional ◽  
Element Abundance ◽  
Late Time ◽  
Chemical Abundance ◽  
Galactocentric Distance ◽  
Gas Accretion ◽  
A Minor

ABSTRACT We investigate the age–chemical abundance structure of the outer Galactic disc at a galactocentric distance of r > 10 kpc as recently revealed by the SDSS/APOGEE survey. Two sequences are present in the [α/Fe]–[Fe/H] plane with systematically different stellar ages. Surprisingly, the young sequence is less metal rich, suggesting a recent dilution process by additional gas accretion. As the stars with the lowest iron abundance in the younger sequence also show an enhancement in α-element abundance, the gas accretion event must have involved a burst of star formation. In order to explain these observations, we construct a chemical evolution model. In this model, we include a relatively short episode of gas accretion at late times on top of an underlying secular accretion over long time-scales. Our model is successful at reproducing the observed distribution of stars in the three-dimensional space of [α/Fe]–[Fe/H]–age in the outer disc. We find that a late-time accretion with a delay of $8.2\,$Gyr and a time-scale of 0.7 Gyr best fits the observed data, in particular the presence of the young, metal-poor sequence. Our best-fitting model further implies that the amount of accreted gas in the late-time accretion event needs to be about three times the local gas reservoir in the outer disc at the time of accretion in order to sufficiently dilute the metal abundance. Given this large fraction, we interpret the late-time accretion event as a minor merger presumably with a gas-rich dwarf galaxy with a mass $M_*\lt 10^{9}\, \mathrm{ M}_{\odot }$ and a gas fraction of ∼75 per cent.

3D modelling of AGB stars with CO5BOLD

2018 ◽  
Vol 14 (S343) ◽  
pp. 9-18
Author(s):  
Bernd Freytag ◽  
Susanne Höfner ◽  
Sofie Liljegren
Keyword(s):  
Radiation Transport ◽  
Three Dimensional ◽  
Asymptotic Giant Branch ◽  
Small Scale ◽  
Dust Formation ◽  
Radiation Hydrodynamics ◽  
Agb Stars ◽  
Outer Atmosphere ◽  
Solar Type ◽  
Dust Distribution

AbstractLocal three-dimensional radiation-hydrodynamics simulations of patches of the surfaces of solar-type stars, that are governed by small-scale granular convection, have helped analyzing and interpreting observations for decades. These models contributed considerably to the understanding of the atmospheres and indirectly also of the interiors and the active layers above the surface of these stars. Of great help was of course the availability of a close-by prototype of these stars – the sun.In the case of an asymptotic-giant-branch (AGB) star, the convective cells have sizes comparable to the radius of the giant. Therefore, the extensions of the solar-type-star simulations to AGB stars have to be global and cover the entire object, including a large part of the convection zone, the molecule-formation layers in the inner atmosphere, and the dust-formation region in the outer atmosphere. Three-dimensional radiation-hydrodynamics simulations with CO5BOLD show how the interplay of large and small convection cells, waves, pulsations, and shocks, but also molecular and dust opacities of AGB stars create conditions very different from those in the solar atmosphere.Recent CO5BOLD models account for frequency-dependent radiation transport and the formation of two independent dust species for an oxygen-rich composition. The drop of the comparably smooth temperature distribution below a threshold determines to onset of dust formation, further in, at higher temperatures, for aluminium oxides (Al2O3) than for silicates (Mg2SiO4). An uneven dust distribution is mostly caused by inhomogeneities in the density of the shocked gas.

scholarly journals Isochrones for late-type stars

2008 ◽  
Vol 4 (S258) ◽  
pp. 383-394 ◽  
Author(s):  
Pierre Demarque
Keyword(s):  
Three Dimensional ◽  
Radiation Hydrodynamics ◽  
Late Type ◽  
Chemical Abundances ◽  
Low Mass Stars ◽  
Structure And Dynamics ◽  
History Of ◽  
Low Mass ◽  
The Subject ◽  
Stellar Interiors

AbstractA brief summary of the history of stellar evolution theory and the use of isochrones is given. The present state of the subject is summarized. The major uncertainties in isochrone construction are considered: chemical abundances and color calibrations, and the treatment of turbulent convection in stellar interior and atmosphere models. The treatment of convection affects the modeling of stellar interiors principally in two ways: convective core overshoot which increases evolutionary lifetimes, and the depth of convection zones which determines theoretical radii. Turbulence also modifies atmospheric structure and dynamics, and the derivation of stellar abundances. The symbiosis of seismic techniques with increasingly more realistic three-dimensional radiation hydrodynamics simulations is transforming the study of late-type stars. The important case of very low mass stars, which are fully convective, is briefly visited.

scholarly journals Simulation Informed CAD for 3D Nanoprinting

Micromachines ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 8 ◽  
Author(s):  
Jason D. Fowlkes ◽  
Robert Winkler ◽  
Eva Mutunga ◽  
Philip D. Rack ◽  
Harald Plank
Keyword(s):  
Analytical Model ◽  
Computer Aided Design ◽  
Critical Mass ◽  
Three Dimensional ◽  
Three Dimensional Objects ◽  
Non Linear ◽  
Out Of Plane ◽  
Digital Scanning ◽  
Definition Of ◽  
Bending Nanowires

A promising 3D nanoprinting method, used to deposit nanoscale mesh style objects, is prone to non-linear distortions which limits the complexity and variety of deposit geometries. The method, focused electron beam-induced deposition (FEBID), uses a nanoscale electron probe for continuous dissociation of surface adsorbed precursor molecules which drives highly localized deposition. Three dimensional objects are deposited using a 2D digital scanning pattern—the digital beam speed controls deposition into the third, or out-of-plane dimension. Multiple computer-aided design (CAD) programs exist for FEBID mesh object definition but rely on the definition of nodes and interconnecting linear nanowires. Thus, a method is needed to prevent non-linear/bending nanowires for accurate geometric synthesis. An analytical model is derived based on simulation results, calibrated using real experiments, to ensure linear nanowire deposition to compensate for implicit beam heating that takes place during FEBID. The model subsequently compensates and informs the exposure file containing the pixel-by-pixel scanning instructions, ensuring nanowire linearity by appropriately adjusting the patterning beam speeds. The derivation of the model is presented, based on a critical mass balance revealed by simulations and the strategy used to integrate the physics-based analytical model into an existing 3D nanoprinting CAD program is overviewed.

Sign in / Sign up

Export Citation Format

Share Document