scholarly journals Comparison of 2D and 3D compressible convection in a pre-main sequence star

2020 ◽  
Vol 638 ◽  
pp. A15
Author(s):  
J. Pratt ◽  
I. Baraffe ◽  
T. Goffrey ◽  
C. Geroux ◽  
T. Constantino ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Convection Zone ◽  
Hydrodynamic Simulations ◽  
3D Simulations ◽  
Stellar Convection ◽  
The Difference ◽  
Set Up ◽  
2D And 3D

Context. A 1D description of stellar dynamics is at the basis of stellar evolution modeling. Designed to investigate open problems in stellar evolution, the MUltidimensional Stellar Implicit Code expands a realistic 1D profile of a star’s internal structure to examine the interior dynamics of a specific star through either 2D or 3D hydrodynamic simulations. Aims. Extending our recent studies of 2D stellar convection to 3D stellar convection, we aim to compare 3D hydrodynamic simulations to identically set-up 2D simulations, for a realistic pre-main sequence star. Methods. We compare statistical quantities related to convective flows including: average velocity, vorticity, local enstrophy, and penetration depth beneath a convection zone. These statistics were produced during stationary, steady-state compressible convection in the star’s convection zone. Results. Our simulations confirm the common result that 2D simulations of stellar convection have a higher magnitude of velocity on average than 3D simulations. Boundary conditions and the extent of the spherical shell can affect the magnitude and variability of convective velocities. The difference between 2D and 3D velocities is dependent on these background points; in our simulations this can have an effect as large as the difference resulting from the dimensionality of the simulation. Nevertheless, radial velocities near the convective boundary are comparable in our 2D and 3D simulations. The average local enstrophy of the flow is lower for 2D simulations than for 3D simulations, indicating a different shape and structuring of 3D stellar convection. We performed a statistical analysis of the depth of convective penetration below the convection zone using the model proposed in our recent study (Pratt et al. 2017, A&A, 604, A125). That statistical model was developed based on 2D simulations, which allowed us to examine longer times and higher radial resolution than are possible in 3D. Here, we analyze the convective penetration in 3D simulations, and compare the results to identically set-up 2D simulations. In 3D simulations, the penetration depth is as large as the penetration depth calculated from 2D simulations.

scholarly journals Observable scattered light features from inclined and non-inclined planets embedded in protoplanetary discs

2019 ◽  
Vol 487 (4) ◽  
pp. 5372-5387
Author(s):  
Dylan L Kloster ◽  
M Flock
Keyword(s):  
Surface Density ◽  
Scattered Light ◽  
Intensity Variation ◽  
Theoretical Models ◽  
Upper Atmosphere ◽  
High Mass ◽  
Hydrodynamic Simulations ◽  
3D Simulations ◽  
2D And 3D ◽  
Protoplanetary Discs

ABSTRACT Over the last few years instruments such as VLT/SPHERE and Subaru/HiCIAO have been able to take detailed scattered light images of protoplanetary discs. Many of the features observed in these discs are generally suspected to be caused by an embedded planet, and understanding the cause of these features requires detailed theoretical models. In this work we investigate disc–planet interactions using the pluto code to run 2D and 3D hydrodynamic simulations of protoplanetary discs with embedded 30 and 300 M⊕ planets on both an inclined (i = 2.86°) and non-inclined orbit, using an α-viscosity of 4 × 10−3. We produce synthetic scattered light images of these discs at H-band wavelengths using the radiative transfer code radmc3d. We find that while the surface density evolution in 2D and 3D simulations of inclined and non-inclined planets remain fairly similar, their observational appearance is remarkably different. Most of the features seen in the synthetic H-band images are connected to density variations of the disc at around 3.3 scale heights above and below the mid-plane, which emphasizes the need for 3D simulations. Planets on sustained orbital inclinations disrupt the disc’s upper atmosphere and produce radically different observable features and intensity profiles, including shadowing effects and intensity variation of the order of 10–20 times the surrounding background. The vertical optical depth to the disc mid-plane for H-band wavelengths is τ ≈ 20 in the disc gap created by the high-mass planet. We conclude that direct imaging of planets embedded in the disc remains difficult to observe, even for massive planets in the gap.

scholarly journals Multidimensional Hydrodynamic and Hydrostatic Stellar Models

2004 ◽  
Vol 215 ◽  
pp. 378-387
Author(s):  
Robert G. Deupree
Keyword(s):  
Stellar Evolution ◽  
Rotation Axis ◽  
Finite Difference Methods ◽  
Stellar Model ◽  
Current Status ◽  
Hydrodynamic Models ◽  
Intermediate Mass ◽  
Hydrodynamic Simulations ◽  
Axis Rotation ◽  
2D And 3D

Results for multidimensional stellar model simulations of both 2D and 3D hydrodynamic models and 2D stellar evolution sequences are presented. Simulations of the highly superadiabatic region of the solar convective region provide a good example of the current status and limitations of explicit 3D finite difference methods in stellar problems. Such simulations cannot be used for stellar cores, where the motion is expected to be well subsonic. The results of some 2D fully implcit hydrodynamic simulations of convective cores and shells are given for models with and without rotation, and their effects examined through fully 2D stellar evolution sequences. One effect of moderate to rapid rotation in convective cores is to alter the convective flow pattern so that convective eddies tend to line up parallel to the rotation axis. Rotation also appears to modestly reduce the amount of convective core overshooting, at least for intermediate mass models.

scholarly journals Posters also presented at the Symposium

2016 ◽  
Vol 12 (S329) ◽  
pp. 455-464
Keyword(s):  
Stellar Evolution ◽  
Scaling Laws ◽  
Convection Zone ◽  
Massive Stars ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Fundamental Properties ◽  
Mass Entrainment ◽  
Nuclear Burning ◽  
Advanced Stages

I am reporting on our team's progress in investigating fundamental properties of convective shells in the deep stellar interior during advanced stages of stellar evolution. We have performed a series of 3D hydrodynamic simulations of convection in conditions similar to those in the O-shell burning phase of massive stars. We focus on characterizing the convective boundary and the mixing of material across this boundary. Results from 7683 and 15363 grids are encouragingly similar (typically within 20%). Several global quantities, including the rate of mass entrainment at the convective boundary and the driving luminosity, are related by scaling laws. We investigate the effect of several of our assumptions, including the treatment of the nuclear burning driving the convection or that of neutrino cooling. The burning of the entrained material from above the convection zone could have important implications for pre-supernova nucleosynthesis.

scholarly journals Interaction of multidimensional convection and radial pulsation

2013 ◽  
Vol 9 (S301) ◽  
pp. 415-416
Author(s):  
Chris M. Geroux ◽  
Robert G. Deupree
Keyword(s):  
3D Models ◽  
Light Curves ◽  
Radial Pulsation ◽  
Spatial Behaviour ◽  
Instability Strip ◽  
Convective Flux ◽  
Hydrodynamic Simulations ◽  
Effective Temperatures ◽  
The Difference ◽  
2D And 3D

AbstractWe have previously calculated a number of 2D hydrodynamic simulations of convection and pulsation to full amplitude. These revealed a significantly better fit to the observed light curves near the red edge of the instability strip in the globular cluster M 3 than did previous 1D mixing length models. Here we compare those 2D results with our new 3D hydrodynamic simulations calculated with the same code. As expected, the horizontal spatial behaviour of convection in 2D and 3D is quite different, but the time dependence of the convective flux on pulsation phase is quite similar. The difference in pulsation growth rate is only about 0.1% per period, with the 3D models having more damping at each of the five effective temperatures considered. Full amplitude pulsation light curves in 2D and 3D are compared.

scholarly journals Main Sequence Evolution, Abundance Anomalies and Particle Transport

2002 ◽  
Vol 12 ◽  
pp. 279-281
Author(s):  
Georges Michaud ◽  
Olivier Richard ◽  
Jacques Richer
Keyword(s):  
Stellar Evolution ◽  
Particle Transport ◽  
Main Sequence ◽  
Convection Zone ◽  
Accurate Determination ◽  
Atomic Diffusion ◽  
Atomic Data ◽  
Data Bases ◽  
Abundance Anomalies

AbstractThe availability of large atomic data bases has made it possible to calculate stellar evolution models taking into detailed account the abundance variations of all important contributors to opacity. In a first step, in addition to nuclear reactions, the atomic diffusion, radiative accelerations and opacity are continuously calculated during evolution taking the abundance changes of 28 species into account. This leads to the first self consistent main sequence stellar evolution models. In A and F stars (M≥ 1.5Mʘ) an iron peak convection zone is shown to appear at a temperature of 200000 K. The calculated surface abundance anomalies, that follow without any arbitrary parameter, are very similar to those observed in AmFm stars in open clusters except that they are larger by a factor of about 3. The second step, is then to introduce a competing hydrodynamical process. To reduce the calculated anomalies to the observed ones, turbulence has been introduced. It is found that the mixed zone must be about 5 times deeper than the iron convection zone. Detailed comparisons to a few AmFm stars have been carried out. The determination of the abundance anomalies of a large number of atomic species (20 to 30 are probably accessible) makes it possible to constrain stellar hydrodynamics. In clusters, the original abundances and age may be known and the accurate determination of surface abundances may constrain turbulence, mass loss and differential rotation when the required atomic data bases are available and used for the modeling of particle transport in stellar evolution.

scholarly journals 3D1D hydro-nucleosynthesis simulations – I. Advective–reactive post-processing method and its application to H ingestion into He-shell flash convection in rapidly accreting white dwarfs

2021 ◽  
Vol 504 (1) ◽  
pp. 744-760 ◽  
Author(s):  
David Stephens ◽  
Falk Herwig ◽  
Paul Woodward ◽  
Pavel Denissenkov ◽  
Robert Andrassy ◽  
...  
Keyword(s):  
Mixing Model ◽  
Post Processing ◽  
Abundance Distribution ◽  
Hydrodynamic Simulations ◽  
3D Simulations ◽  
Energy Feedback ◽  
Mixing Coefficients ◽  
The Difference ◽  
Advective Mixing ◽  
Stream Model

ABSTRACT We present two mixing models for post-processing of 3D hydrodynamic simulations applied to convective–reactive i-process nucleosynthesis in a rapidly accreting white dwarf (RAWD) with [Fe/H] = −2.6, in which H is ingested into a convective He shell. A 1D advective two-stream model adopts physically motivated radial and horizontal mixing coefficients constrained by 3D hydrodynamic simulations. A simpler approach uses diffusion coefficients calculated from the same simulations. All 3D simulations include the energy feedback of the 12C(p, γ)13N reaction from the H entrainment. Global oscillations of shell H ingestion in two of the RAWD simulations cause bursts of entrainment of H and non-radial hydrodynamic feedback. With the same nuclear network as in the 3D simulations, the 1D advective two-stream model reproduces the rate and location of the H burning within the He shell closely matching the 3D simulation predictions, as well as qualitatively displaying the asymmetry of the XH profiles between the upstream and downstream. With a full i-process network the advective mixing model captures the difference in the n-capture nucleosynthesis in the upstream and downstream. For example, 89Kr and 90Kr with half-lives of $3.18\,\,\mathrm{\mathrm{min}}$ and $32.3\,\,\mathrm{\mathrm{s}}$ differ by a factor 2–10 in the two streams. In this particular application the diffusion approach provides globally the same abundance distribution as the advective two-stream mixing model. The resulting i-process yields are in excellent agreement with observations of the exemplary CEMP-r/s star CS31062-050.

scholarly journals The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

2016 ◽  
Vol 591 ◽  
pp. L6 ◽  
Author(s):  
A. Irrgang ◽  
A. Desphande ◽  
S. Moehler ◽  
M. Mugrauer ◽  
D. Janousch
Keyword(s):  
Stellar Evolution ◽  
Main Sequence

Experimental Investigation into Driver Behavior along Curved and Parallel Diverging Terminals of Exit Interchange Ramps

2021 ◽  
pp. 036119812199742
Author(s):  
Alberto Portera ◽  
Marco Bassani
Keyword(s):  
Design Stage ◽  
Lane Change ◽  
Age And Gender ◽  
Traffic Conditions ◽  
Current Design ◽  
The Difference ◽  
Safety Countermeasures ◽  
And Gender ◽  
Set Up ◽  
Curve Radius

Current design manuals provide guidance on how to design exit ramps to facilitate driving operations and minimize the incidence of crashes. They also suggest that interchanges should be built along straight roadway sections. These criteria may prove ineffective in situations where there is no alternative to terminals being located along curved motorway segments. The paper investigates driving behavior along parallel deceleration curved terminals, with attention paid to the difference in impact between terminals having a curvature which is the same sign as the motorway segment (i.e., continue design), and those having an opposite curvature (i.e., reverse design). A driving simulation study was set up to collect longitudinal and transversal driver behavioral data in response to experimental factor variations. Forty-eight drivers were stratified on the basis of age and gender, and asked to drive along three randomly assigned circuits with off-ramps obtained by combining experimental factors such as motorway mainline curve radius (2 values), terminal length (3), curve direction (2), and traffic conditions (2). The motorway radius was found to be significant for drivers’ preferred speed when approaching the terminal. Terminal length and traffic volume do not have a significant impact on either longitudinal or transversal driver outputs. However, the effect of curve direction was found to be significant, notably for reverse terminals which do not compel drivers to select appropriate speeds and lane change positions. This terminal type can give rise to critical driving situations that should be considered at the design stage to facilitate the adoption of appropriate safety countermeasures.

scholarly journals Possible Global Magneto-Fluid Structure of the Stellar Convection Zone

2006 ◽  
Vol 58 (3) ◽  
pp. 605-616 ◽  
Author(s):  
Sanae I. Itoh ◽  
Kimitaka Itoh ◽  
Patrick H. Diamond ◽  
Akira Yoshizawa
Keyword(s):  
Convection Zone ◽  
Fluid Structure ◽  
Stellar Convection

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

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