scholarly journals Meridional Circulation of Dust and Gas in the Circumstellar Disk: Delivery of Solids onto the Circumplanetary Region

2022 ◽  
Vol 924 (1) ◽  
pp. 1
Author(s):  
J. Szulágyi ◽  
F. Binkert ◽  
C. Surville
Keyword(s):  
Meridional Circulation ◽  
Circumstellar Disk ◽  
Hydrodynamic Simulations ◽  
Planetary Mass ◽  
Accretion Rates ◽  
The Difference ◽  
Local Dust ◽  
Gas Accretion ◽  
The Hill ◽  
Gas Ratio

Abstract We carried out 3D dust + gas radiative hydrodynamic simulations of forming planets. We investigated a parameter grid of a Neptune-mass, a Saturn-mass, a Jupiter-mass, and a five-Jupiter-mass planet at 5.2, 30, and 50 au distance from their star. We found that the meridional circulation (Szulágyi et al. 2014; Fung & Chiang 2016) drives a strong vertical flow for the dust as well, hence the dust is not settled in the midplane, even for millimeter-sized grains. The meridional circulation will deliver dust and gas vertically onto the circumplanetary region, efficiently bridging over the gap. The Hill-sphere accretion rates for the dust are ∼10−8–10−10 M Jup yr−1, increasing with planet mass. For the gas component, the gain is 10−6–10−8 M Jup yr−1. The difference between the dust and gas-accretion rates is smaller with decreasing planetary mass. In the vicinity of the planet, the millimeter-sized grains can get trapped easier than the gas, which means the circumplanetary disk might be enriched with solids in comparison to the circumstellar disk. We calculated the local dust-to-gas ratio (DTG) everywhere in the circumstellar disk and identified the altitude above the midplane where the DTG is 1, 0.1, 0.01, and 0.001. The larger the planetary mass, the more the millimeter-sized dust is delivered and a larger fraction of the dust disk is lifted by the planet. The stirring of millimeter-sized dust is negligible for Neptune-mass planets or below, but significant above Saturn-mass planets.

scholarly journals Gas flow around a planet embedded in a protoplanetary disc

2019 ◽  
Vol 623 ◽  
pp. A179 ◽  
Author(s):  
Ayumu Kuwahara ◽  
Hiroyuki Kurokawa ◽  
Shigeru Ida
Keyword(s):  
Gas Flow ◽  
Three Dimensional ◽  
Stokes Number ◽  
Dimensional Structure ◽  
Solid Materials ◽  
Planetary Mass ◽  
Short Period ◽  
Hydrodynamical Simulations ◽  
Gas Accretion ◽  
The Hill

Context. The ubiquity of short-period super-Earths remains a mystery in planet formation, as these planets are expected to become gas giants via runaway gas accretion within the lifetime of a protoplanetary disc. The cores of super-Earths should form in the late stage of disc evolution to avoid runaway gas accretion. Aims. The three-dimensional structure of the gas flow around a planet is thought to influence the accretion of both gas and solid materials. In particular, the outflow in the midplane region may prevent the accretion of solid materials and delay the formation of the super-Earth cores. However, it is not yet understood how the nature of the flow field and outflow speed change as a function of the planetary mass. In this study, we investigate the dependence of gas flow around a planet embedded in a protoplanetary disc on the planetary mass. Methods. Assuming an isothermal, inviscid gas disc, we perform three-dimensional hydrodynamical simulations on the spherical polar grid, which has a planet located at its centre. Results. We find that gas enters the Bondi or Hill sphere at high latitudes and exits through the midplane region of the disc regardless of the assumed dimensionless planetary mass m = RBondi∕H, where RBondi and H are the Bondi radius of the planet and disc scale height, respectively. The altitude from where gas predominantly enters the envelope varies with planetary mass. The outflow speed can be expressed as |uout| = √3/2mcs (RBondi ≤ RHill) or |uout| = √3/2(m/3)1/3cs (RBondi ≥ RHill), where cs is the isothermal sound speed and RHill is the Hill radius. The outflow around a planet may reduce the accretion of dust and pebbles onto the planet when m ≳ √St, where S t is the Stokes number. Conclusions. Our results suggest that the flow around proto-cores of super-Earths may delay their growth and consequently help them to avoid runaway gas accretion within the lifetime of the gas disc.

scholarly journals Global 3D radiation-hydrodynamic simulations of gas accretion: Opacity-dependent growth of Saturn-mass planets

2019 ◽  
Vol 632 ◽  
pp. A118 ◽  
Author(s):  
M. Schulik ◽  
A. Johansen ◽  
B. Bitsch ◽  
E. Lega
Keyword(s):  
Gas Flow ◽  
Temporal Evolution ◽  
Accretion Rate ◽  
Hydrodynamic Simulations ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Energy Sink ◽  
Dependent Growth ◽  
Self Gravity ◽  
Gas Accretion

The full spatial structure and temporal evolution of the accretion flow into the envelopes of growing gas giants in their nascent discs is only accessible in simulations. Such simulations are constrained in their approach of computing the formation of gas giants by dimensionality, resolution, consideration of self-gravity, energy treatment and the adopted opacity law. Our study explores how a number of these parameters affect the measured accretion rate of a Saturn-mass planet. We present a global 3D radiative hydrodynamics framework using the FARGOCA-code. The planet is represented by a gravitational potential with a smoothing length at the location of the planet. No mass or energy sink is used; instead luminosity and gas accretion rates are self-consistently computed. We find that the gravitational smoothing length must be resolved by at least ten grid cells to obtain converged measurements of the gas accretion rates. Secondly, we find gas accretion rates into planetary envelopes that are compatible with previous studies, and continue to explain those via the structure of our planetary envelopes and their luminosities. Our measured gas accretion rates are formally in the stage of Kelvin–Helmholtz contraction due to the modest entropy loss that can be obtained over the simulation timescale, but our accretion rates are compatible with those expected during late run-away accretion. Our detailed simulations of the gas flow into the envelope of a Saturn-mass planet provide a framework for understanding the general problem of gas accretion during planet formation and highlight circulation features that develop inside the planetary envelopes. Those circulation features feedback into the envelope energetics and can have further implications for transporting dust into the inner regions of the envelope.

Cyanoacrylate Inhibitors of the Hill Reaction V. The Effect of Chirality on Inhibitor Binding

1987 ◽  
Vol 42 (6) ◽  
pp. 684-689 ◽  
Author(s):  
John L. Huppatz ◽  
John N. Phillips
Keyword(s):  
Phenyl Ring ◽  
Alkyl Substituent ◽  
Receptor Site ◽  
Optically Active ◽  
Hill Reaction ◽  
Inhibitor Binding ◽  
Level Of Activity ◽  
The Difference ◽  
The Hill

Optically active α-methylbenzylamino 2-cyanoacrylic esters were synthesized and assayed as inhibitors of the Hill reaction in isolated pea chloroplast fragments. The 5-isomers were more potent inhibitors than the S-isomers with discriminations of from ten to greater than 100-fold being observed. A β-alkyl substituent in the cyanoacrylate molecule affected both the level of activity and the difference in activity between the isomers. An α,α-dimethylbenzylamino derivative was also active at about the same level as the corresponding α-methylbenzylamino racemate. This result could be explained in terms of the orientation of the phenyl ring in the receptor site. Replacement of the α-methylbenzylamino group by other α-alkyl and α-phenyl substituents had little effect on activity. However, an α-benzyl group was beneficial.

scholarly journals GJ 436b and the stellar wind interaction: simulations constraints using Lyα and Hα transits

2020 ◽  
Author(s):  
Carolina Villarreal D’Angelo ◽  
Aline A Vidotto ◽  
Alejandro Esquivel ◽  
Gopal Hazra ◽  
Allison Youngblood
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Planetary System ◽  
Neutral Hydrogen ◽  
Hydrogen Atmosphere ◽  
Planetary Atmosphere ◽  
Hydrodynamic Simulations ◽  
Stellar Disc ◽  
Planetary Mass ◽  
Best Fit

Abstract The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Lyα line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the $\sim 56\%$ absorption found in Lyα transits, simultaneously with the lack of absorption in Hα transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Lyα observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s−1 with a temperature of [3 − 4] × 105 K. The stellar and planetary mass loss rates are found to be 2 × 10−15 M⊙ yr−1 and ∼[6 − 10] × 109 g s−1, respectively, for a stellar EUV luminosity of [0.8 − 1.6] × 1027 erg s−1. For the parameters explored in our simulations, none of our models present any significant absorption in the Hα line in agreement with the observations.

scholarly journals Influence of migration models and thermal torque on planetary growth in the pebble accretion scenario

2020 ◽  
Vol 637 ◽  
pp. A11 ◽  
Author(s):  
Thomas Baumann ◽  
Bertram Bitsch
Keyword(s):  
Planet Formation ◽  
Major Axis ◽  
Type I ◽  
Semi Major Axis ◽  
Disk Structure ◽  
Accretion Rates ◽  
Low Mass ◽  
Planetary Migration ◽  
Gas Accretion ◽  
Outward Migration

Low-mass planets that are in the process of growing larger within protoplanetary disks exchange torques with the disk and change their semi-major axis accordingly. This process is called type I migration and is strongly dependent on the underlying disk structure. As a result, there are many uncertainties about planetary migration in general. In a number of simulations, the current type I migration rates lead to planets reaching the inner edge of the disk within the disk lifetime. A new kind of torque exchange between planet and disk, the thermal torque, aims to slow down inward migration via the heating torque. The heating torque may even cause planets to migrate outwards, if the planetary luminosity is large enough. Here, we study the influence on planetary migration of the thermal torque on top of previous type I models. We find that the formula of Paardekooper et al. (2011, MNRAS, 410, 293) allows for more outward migration than that of Jiménez & Masset (2017, MNRAS, 471, 4917) in most configurations, but we also find that planets evolve to very similar mass and final orbital radius using both formulae in a single planet-formation scenario, including pebble and gas accretion. Adding the thermal torque can introduce new, but small, regions of outwards migration if the accretion rates onto the planet correspond to typical solid accretion rates following the pebble accretion scenario. If the accretion rates onto the planets become very large, as could be the case in environments with large pebble fluxes (e.g., high-metallicity environments), the thermal torque can allow more efficient outward migration. However, even then, the changes for the final mass and orbital positions in our planet formation scenario are quite small. This implies that for single planet evolution scenarios, the influence of the heating torque is probably negligible.

Mass Transfer in Mira-Type Binaries

2012 ◽  
Vol 21 (1-2) ◽  
Author(s):  
S. Mohamed ◽  
Ph. Podsiadlowski
Keyword(s):  
Mass Transfer ◽  
Orbital Plane ◽  
Planetary Nebulae ◽  
Transfer Rates ◽  
Hydrodynamic Simulations ◽  
Transfer Mode ◽  
Mass Transfer Mechanism ◽  
Accretion Rates ◽  
Order Of Magnitude ◽  
Symbiotic Binaries

AbstractDetached, symbiotic binaries are generally assumed to interact via Bondi-Hoyle-Littleton (BHL) wind accretion. However, the accretion rates and outflow geometries that result from this mass-transfer mechanism cannot adequately explain the observations of the nearest and best studied symbiotic binary, Mira, or the formation of some post-AGB binaries, e.g. barium stars. We propose a new mass-transfer mode for Mira-type binaries, which we call ‘wind Roche-lobe overflow’ (WRLOF), and which we demonstrate with 3D hydrodynamic simulations. Importantly, we show that the circumstellar outflows which result from WRLOF tend to be highly aspherical and strongly focused towards the binary orbital plane. Furthermore, the subsequent mass-transfer rates are at least an order of magnitude greater than the analogous BHL values. We discuss the implications of these results for the shaping of bipolar (proto)-planetary nebulae and other related systems.

scholarly journals Two-Dimensional Accretion Disk Models of a Neutron Star

1998 ◽  
Vol 188 ◽  
pp. 374-375
Author(s):  
M. Fujita ◽  
T. Okuda
Keyword(s):  
Neutron Star ◽  
Electron Scattering ◽  
Radiation Transport ◽  
Compact Object ◽  
Compact Objects ◽  
High Mass ◽  
Two Dimensional ◽  
Accretion Rates ◽  
The Difference ◽  
Characteristic Features

We investigate the accretion disks around compact objects with high mass accretion rates near the Eddington's critical value ME, where radiation pressure and electron scattering are dominant. This raises next problems: (a) whether stable disks could exist in relation to the theory of thermal instabilities of the disk and (b) what characteristic features the disks have if the stable disks exist. A non-rotating neutron star with the mass M = 1.4M⊙, radius R* = 107cm and the accretion rate Mac = 2.0 and 0.5Mac (models 1 and 2) is considered as the compact object. We assume the α-model for the viscosity and solve the set of two-dimensional time-dependent hydrodynamic equations coupled with radiation transport. The numerical method used is basically the same as one described by Kley and Hensler (1987) and Kley (1989) but we include some improvements in solving the difference equations (Okuda et al. 1997). The initial configuration consists of a cold, dense, and optically thick disk which is given by the standard α-model (Shakura and Sunyaev 1973) and a rarefied optically thin atmosphere around the disk.

Discovery of a Planetary-Mass Brown Dwarf with a Circumstellar Disk

2005 ◽  
Vol 635 (1) ◽  
pp. L93-L96 ◽  
Author(s):  
K. L. Luhman ◽  
Lucía Adame ◽  
Paola D'Alessio ◽  
Nuria Calvet ◽  
Lee Hartmann ◽  
...  
Keyword(s):  
Circumstellar Disk ◽  
Brown Dwarf ◽  
Planetary Mass

scholarly journals The effect of gas accretion on the radial gas metallicity profile of simulated galaxies

2020 ◽  
Vol 495 (3) ◽  
pp. 2827-2843 ◽  
Author(s):  
Florencia Collacchioni ◽  
Claudia D P Lagos ◽  
Peter D Mitchell ◽  
Joop Schaye ◽  
Emily Wisnioski ◽  
...  
Keyword(s):  
Star Formation Rate ◽  
Accretion Rate ◽  
Formation Rate ◽  
Main Property ◽  
Stellar Mass ◽  
Effective Radius ◽  
Mass Star ◽  
Hydrodynamic Simulations ◽  
Gas Accretion ◽  
Gas Fractions

ABSTRACT We study the effect of the gas accretion rate ($\dot{M}_{\rm accr}$) on the radial gas metallicity profile (RMP) of galaxies using the eagle cosmological hydrodynamic simulations, focusing on central galaxies of stellar mass M⋆ ≳ 109 M⊙ at z ≤ 1. We find clear relations between $\dot{M}_{\rm accr}$ and the slope of the RMP (measured within an effective radius), where higher $\dot{M}_{\rm accr}$ are associated with more negative slopes. The slope of the RMPs depends more strongly on $\dot{M}_{\rm accr}$ than on stellar mass, star formation rate (SFR), or gas fraction, suggesting $\dot{M}_{\rm accr}$ to be a more fundamental driver of the RMP slope of galaxies. We find that eliminating the dependence on stellar mass is essential for pinning down the properties that shape the slope of the RMP. Although $\dot{M}_{\rm accr}$ is the main property modulating the slope of the RMP, we find that it causes other correlations that are more easily testable observationally: At fixed stellar mass, galaxies with more negative RMP slopes tend to have higher gas fractions and SFRs, while galaxies with lower gas fractions and SFRs tend to have flatter metallicity profiles within an effective radius.

Kinetics of volume-sensitive K transport in human erythrocytes: evidence for asymmetry

1989 ◽  
Vol 256 (6) ◽  
pp. C1214-C1223 ◽  
Author(s):  
D. M. Kaji
Keyword(s):  
Statistical Significance ◽  
High Capacity ◽  
Human Erythrocytes ◽  
Kinetic Properties ◽  
Maximal Velocity ◽  
Hill Coefficients ◽  
The Difference ◽  
K Concentration ◽  
The Hill ◽  
External K

The kinetic properties of volume-sensitive K fluxes in swollen human erythrocytes were investigated. Swelling-activated Cl-dependent K influx was a saturable function of external K concentration with a low affinity (apparent Km of 115-130 mM) and high capacity [maximal velocity (Vmax) = 20-30 mmol.l original cells-1.h-1 (mmol.loc-1.h-1)]. The Vmax and apparent Km for Cl-dependent K efflux were lower (Km = 47 mM; Vmax = 2.2 mmol.loc-1.h-1). The Hill coefficients for both K efflux and influx were close to unity, suggesting a single binding site for K. The increase of external K trans-stimulated K efflux, but the increase of intracellular K had no effect on Cl-dependent K influx in swollen cells. Under zero trans conditions, the Vmax (18 vs. 3 mmol.loc-1.h-1) and Km (138 vs. 32) were markedly different for influx and efflux, respectively. These results provide evidence for intrinsic functional asymmetry, such that the transporter is more prevalent and stable in the outward-facing conformation. The mean ratio of Km to Vmax for efflux (12.1) was 1.56 times larger than the same ratio for influx (7.8), but the difference between the means did not reach statistical significance. These kinetic observations are analyzed in terms of the simple carrier and the cotransport models.

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