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Stellar Hydrodynamics

Together with Paul Woodward and his group we are investigating stellar interior convection with nuclear burning at Damköhler numbers ~1, i.e. nuclear burn time scale and convective mixing time scale are similar. The ultimate goal is to develop a better understanding of convective mixing in stellar evolution, and the formation of the elements in the first generations of stars, where this nucleosynthesis and hydrodynamics regime is believed to be important.


Movies available at the LCSE site
Movies of stellar hydrodynamics simulations, especially those computed with the highest resolution, can be found at Paul Woodward's page at the LCSE, University of Minnesota.
H-ingestion in AGB He-shell
Movies of fractional volume (concentration) of H-rich material entrained and ingested into AGB He-shell flash convection, and burning of H-rich material in layers deep enough to have high enough T for reactions to occur on advection time scale. Shown is the initial quiescent phase of ingestion of burning, before the onset of the global oscillation in H-ingestion shell convection. The movie combines both time evolutions as well as variable viewing angles and mask settings for a given frame. The goal of this movie is to demonstrate the global nature of the entrainment process and the large-scale correlations of H-enriched flow structures descending down into the hotter regions of He-shell flash convection. A movie with an alternative color scheme is available as well. This 768^3-grid run has been performed on ComputeCanada WestGrid resources.
H-ingestion simulation for Sakurai's object
Similar to the AGB He-shell H-ingestion simulation, but for the stratification that is exactly the same as our previous stellar evolution (Herwig 2001) and multi-zone nucleosynthesis (Herwig+ 11) simulations of Sakurai's object. As described in our GOSH paper (Herwig+ 13, arXiv:1310.4584) the initial quiescent phase of H-ingestion entrainment is followed by a violent rearrangement of the convective structure of the He-shell flash convection zone via a global oscillation of shell H-ingestion. This 768^3 simulation has been performed on ComputeCanada/WestGrid computers using the PPMstar code developed by Paul Woodward.
More movies
Links to movies provided in other directories.
O-shell convection movies
Movies related to Jones et al. 2017, MNRAS: Idealised hydrodynamic simulations of O-shell convection in 4π geometry

Idealised hydrodynamic simulations of turbulent oxygen-burning shell convection in 4π geometry

Project summary
We investigate convective boundary mixing at the top of an idealised O-burning shell using 3D hydrodynamic simulations.
About the simulation codes
We use the 1D stellar evolution code MESA and 3D hydrodynamic code PPMstar.
Images and movies
Link to paper

Global non-spherical oscillations in 3-D 4π simulations of the H-ingestion flash

Preprint on astro-ph
Project summary
3D PPM hydrodynamic simulations of H-ingestion into He-shell flash convection for a very-late thermal pulse (He-shell flash) model of Sakurai's object.
Images and movies

3-D star He-shell flash convection and H entrainment

Detailed description of the entrainment process in converged 3-D simulations in full spherical geometry.
Project summary
In this paper Woodward, Herwig & Lin demonstrate the PPMstar capabiltiy to construct converged entrainment simulations at the extremely stiff upper convective boundary when H-rich material may be ingested. This situation occurs in very-late thermal pulse post-AGB stars and in low-Z AGB stars. As an important result we provide evidence that full 4Pi geometry and 3-D simulations are required for H-ingestion simulations, and we provide a quantitative entrainment rate from our simulations. The numerical method is described in detail
Images and Movies
FileApJ paper pdf
Paul R. Woodward et al. 2015 ApJ 798 49. doi:10.1088/0004-637X/798/1/49, Received 14 July 2013, accepted for publication 12 August 2014. Published 19 December 2014.

Convective-reactive Proton-C12 Combustion in Sakurai's Object (V4334 Sagittarii) and Implications for the Evolution and Yields from the First Generations of Stars

Project summary
We perform multi-zone nucleosynthesis simulations based on a one-dimensional stellar evolution model of Sakurai's object, a post-AGB stars that has experienced a He-shell flash during the young white dwarf stage. The simulation results, including ehavy elements like Rb, Sr, Ba and La are compared to observations of this particular object, and important conclusions and constraints for the hydrodynamic nature and the physics of H-ingestion flashes and convective-reactive episodes in stellar environments are reached.
About the simulation codes
We used the stellar evolution code EVOL, the NuGrid nucleosynthesis codes and the PPMstar hydrodynamics code.
Images and movies
Link to paper