scholarly journals Linking 1D Stellar Evolution to 3D Hydrodynamic Simulations

2014 ◽  
Vol 9 (S307) ◽  
pp. 98-99 ◽  
Author(s):  
A. Cristini ◽  
R. Hirschi ◽  
C. Georgy ◽  
C. Meakin ◽  
D. Arnett ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Richardson Number ◽  
Front Propagation ◽  
Bulk Richardson Number ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Boundary Mixing ◽  
The Core ◽  
Convective Boundaries ◽  
Initial Results

AbstractIn this contribution we present initial results of a study on convective boundary mixing (CBM) in massive stellar models using the GENEVA stellar evolution code (Eggenbergeret al.2008). Before undertaking costly 3D hydrodynamic simulations, it is important to study the general properties of convective boundaries, such as the: composition jump; pressure gradient; and “stiffness”. Models for a 15M⊙star were computed. We found that for convective shells above the core, the lower (in radius or mass) boundaries are “stiffer” according to the bulk Richardson number than the relative upper (Schwarzschild) boundaries. Thus, we expect reduced CBM at the lower boundaries in comparison to the upper. This has implications on flame front propagation and the onset of novae.

scholarly journals AGB star models. Results from 1D stellar evolution and multi-dimensional hydrodynamics simulations

2008 ◽  
Vol 4 (S252) ◽  
pp. 205-213 ◽  
Author(s):  
Falk Herwig
Keyword(s):  
Stellar Evolution ◽  
Internal Gravity Waves ◽  
Agb Stars ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Boundary Mixing ◽  
Star Models ◽  
Current State ◽  
Low Metallicity ◽  
Internal Evolution

AbstractIn this review I am discussing the current state of simulating the internal evolution of AGB stars. Recent work on AGB stars include the effect of rotation, magnetic fields and internal gravity waves, as well as thermohaline mixing induced by the 3He + 3He pp-chain reaction. Hydrodynamic simulations of the interior convection of AGB stars are now becoming available, giving insights to convective boundary mixing, for example for He-shell flash convection. At very low metallicity convective-reactive events are encountered in AGB stars (as well as in massive stars), and the necessity of hydrodynamic simulations to address this difficult phase of stellar evolution is emphasized.

scholarly journals Progenitors of Core-Collapse Supernovae

2017 ◽  
Vol 12 (S331) ◽  
pp. 1-10
Author(s):  
R. Hirschi ◽  
D. Arnett ◽  
A. Cristini ◽  
C. Georgy ◽  
C. Meakin ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Core Collapse ◽  
Strong Impact ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Boundary Mixing ◽  
Intermediate Mass Stars ◽  
Key Points ◽  
Carbon Burning

AbstractMassive stars have a strong impact on their surroundings, in particular when they produce a core-collapse supernova at the end of their evolution. In these proceedings, we review the general evolution of massive stars and their properties at collapse as well as the transition between massive and intermediate-mass stars. We also summarise the effects of metallicity and rotation. We then discuss some of the major uncertainties in the modelling of massive stars, with a particular emphasis on the treatment of convection in 1D stellar evolution codes. Finally, we present new 3D hydrodynamic simulations of convection in carbon burning and list key points to take from 3D hydrodynamic studies for the development of new prescriptions for convective boundary mixing in 1D stellar evolution codes.

scholarly journals Relative importance of convective uncertainties in massive stars

2020 ◽  
Vol 496 (2) ◽  
pp. 1967-1989 ◽  
Author(s):  
Etienne A Kaiser ◽  
Raphael Hirschi ◽  
W David Arnett ◽  
Cyril Georgy ◽  
Laura J A Scott ◽  
...  
Keyword(s):  
Convective Zone ◽  
Stellar Structure ◽  
Convective Boundary ◽  
Hydrogen Burning ◽  
Surface Evolution ◽  
Boundary Mixing ◽  
The Core ◽  
Boundary Location ◽  
Parameter Values ◽  
The Impact

ABSTRACT In this work, we investigate the impact of uncertainties due to convective boundary mixing (CBM), commonly called ‘overshoot’, namely the boundary location and the amount of mixing at the convective boundary, on stellar structure and evolution. For this we calculated two grids of stellar evolution models with the MESA code, each with the Ledoux and the Schwarzschild boundary criterion, and vary the amount of CBM. We calculate each grid with the initial masses of 15, 20, and $25\, \rm {M}_\odot$. We present the stellar structure of the models during the hydrogen and helium burning phases. In the latter, we examine the impact on the nucleosynthesis. We find a broadening of the main sequence with more CBM, which is more in agreement with observations. Furthermore, during the core hydrogen burning phase there is a convergence of the convective boundary location due to CBM. The uncertainties of the intermediate convective zone remove this convergence. The behaviour of this convective zone strongly affects the surface evolution of the model, i.e. how fast it evolves redwards. The amount of CBM impacts the size of the convective cores and the nucleosynthesis, e.g. the 12C to 16O ratio and the weak s-process. Lastly, we determine the uncertainty that the range of parameter values investigated introduces and we find differences of up to $70{{\ \rm per\ cent}}$ for the core masses and the total mass of the star.

scholarly journals Convective boundary mixing in low- and intermediate-mass stars – I. Core properties from pressure-mode asteroseismology

2020 ◽  
Vol 493 (4) ◽  
pp. 4987-5004 ◽  
Author(s):  
George C Angelou ◽  
Earl P Bellinger ◽  
Saskia Hekker ◽  
Alexey Mints ◽  
Yvonne Elsworth ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Measurement Precision ◽  
Observational Constraints ◽  
Intermediate Mass ◽  
Convective Boundary ◽  
Mode Identification ◽  
Boundary Mixing ◽  
Intermediate Mass Stars ◽  
F Stars

ABSTRACT Convective boundary mixing (CBM) is ubiquitous in stellar evolution. It is a necessary ingredient in the models in order to match observational constraints from clusters, binaries, and single stars alike. We compute ‘effective overshoot’ measures that reflect the extent of mixing and which can differ significantly from the input overshoot values set in the stellar evolution codes. We use constraints from pressure modes to infer the CBM properties of Kepler and CoRoT main-sequence and subgiant oscillators, as well as in two radial velocity targets (Procyon A and α Cen A). Collectively, these targets allow us to identify how measurement precision, stellar spectral type, and overshoot implementation impact the asteroseismic solution. With these new measures, we find that the ‘effective overshoot’ for most stars is in line with physical expectations and calibrations from binaries and clusters. However, two F-stars in the CoRoT field (HD 49933 and HD 181906) still necessitate high overshoot in the models. Due to short mode lifetimes, mode identification can be difficult in these stars. We demonstrate that an incongruence between the radial and non-radial modes drives the asteroseismic solution to extreme structures with highly efficient CBM as an inevitable outcome. Understanding the cause of seemingly anomalous physics for such stars is vital for inferring accurate stellar parameters from TESS data with comparable timeseries length.

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 Impact of convective boundary mixing on the TP-AGB

2020 ◽  
Vol 493 (4) ◽  
pp. 4748-4762
Author(s):  
G Wagstaff ◽  
M M Miller Bertolami ◽  
A Weiss
Keyword(s):  
Surface Composition ◽  
Mass Range ◽  
Asymptotic Giant Branch ◽  
Observational Constraints ◽  
Theoretical Argument ◽  
Convective Boundary ◽  
Convective Envelope ◽  
Boundary Mixing ◽  
Turbulent Entrainment ◽  
Convective Boundaries

ABSTRACT The treatment of convective boundaries remains an important source of uncertainty within stellar evolution, with drastic implications for the thermally pulsing stars on the asymptotic giant branch (AGB). Various sources are taken as motivation for the incorporation of convective boundary mixing (CBM) during this phase, from s-process nucleosynthesis to hydrodynamical models. In spite of the considerable evidence in favour of the existence of CBM on the pre-AGB evolution, this mixing is not universally included in models of TP-AGB stars. The aim of this investigation is to ascertain the extent of CBM, which is compatible with observations when considering full evolutionary models. Additionally, we investigate a theoretical argument that has been made that momentum-driven overshooting at the base of the pulse-driven convection zone should be negligible. We show that, while the argument holds, it would similarly limit mixing from the base of the convective envelope. On the other hand, estimations based on the picture of turbulent entrainment suggest that mixing is possible at both convective boundaries. We demonstrate that additional mixing at convective boundaries during core-burning phases prior to the thermally pulsing AGB has an impact on the later evolution, changing the mass range at which the third dredge-up and hot-bottom burning occur, and thus also the final surface composition. In addition, an effort has been made to constrain the efficiency of CBM at the different convective boundaries, using observational constraints. Our study suggests a strong tension between different constraints that makes it impossible to reproduce all observables simultaneously within the framework of an exponentially decaying overshooting. This result calls for a reassessment of both the models of CBM and the observational constraints.

scholarly journals The i-process yields of rapidly accreting white dwarfs from multicycle He-shell flash stellar evolution models with mixing parametrizations from 3D hydrodynamics simulations

2019 ◽  
Vol 488 (3) ◽  
pp. 4258-4270 ◽  
Author(s):  
Pavel A Denissenkov ◽  
Falk Herwig ◽  
Paul Woodward ◽  
Robert Andrassy ◽  
Marco Pignatari ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
White Dwarfs ◽  
Binary Systems ◽  
Scaling Laws ◽  
Ingestion Rate ◽  
Three Dimensional ◽  
Close Binary ◽  
Convective Boundary ◽  
Retention Efficiency ◽  
Hydrodynamic Simulations

ABSTRACT We have modelled the multicycle evolution of rapidly accreting CO white dwarfs (RAWDs) with stable H burning intermittent with strong He-shell flashes on their surfaces for 0.7 ≤ MRAWD/M⊙ ≤ 0.75 and [Fe/H] ranging from 0 to −2.6. We have also computed the i-process nucleosynthesis yields for these models. The i process occurs when convection driven by the He-shell flash ingests protons from the accreted H-rich surface layer, which results in maximum neutron densities Nn, max ≈ 1013–1015 cm−3. The H-ingestion rate and the convective boundary mixing (CBM) parameter ftop adopted in the one-dimensional nucleosynthesis and stellar evolution models are constrained through three-dimensional (3D) hydrodynamic simulations. The mass ingestion rate and, for the first time, the scaling laws for the CBM parameter ftop have been determined from 3D hydrodynamic simulations. We confirm our previous result that the high-metallicity RAWDs have a low mass retention efficiency ($\eta \lesssim 10{{\ \rm per\ cent}}$). A new result is that RAWDs with [Fe/H] $\lesssim -2$ have $\eta \gtrsim 20{{\ \rm per\ cent}}$; therefore, their masses may reach the Chandrasekhar limit and they may eventually explode as SNeIa. This result and the good fits of the i-process yields from the metal-poor RAWDs to the observed chemical composition of the CEMP-r/s stars suggest that some of the present-day CEMP-r/s stars could be former distant members of triple systems, orbiting close binary systems with RAWDs that may have later exploded as SNeIa.

scholarly journals The First 3D Simulations of Carbon Burning in a Massive Star

2016 ◽  
Vol 12 (S329) ◽  
pp. 237-241 ◽  
Author(s):  
A. Cristini ◽  
C. Meakin ◽  
R. Hirschi ◽  
D. Arnett ◽  
C. Georgy ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Radial Profile ◽  
Three Dimensional ◽  
Stable Region ◽  
Entrainment Rate ◽  
Convective Boundary ◽  
Boundary Mixing ◽  
Turbulent Entrainment ◽  
Large Eddy ◽  
Carbon Burning

AbstractWe present the first detailed three-dimensional hydrodynamic implicit large eddy simulations of turbulent convection for carbon burning. The simulations start with an initial radial profile mapped from a carbon burning shell within a 15 M⊙stellar evolution model. We considered 4 resolutions from 1283to 10243zones. These simulations confirm that convective boundary mixing (CBM) occurs via turbulent entrainment as in the case of oxygen burning. The expansion of the boundary into the surrounding stable region and the entrainment rate are smaller at the bottom boundary because it is stiffer than the upper boundary. The results of this and similar studies call for improved CBM prescriptions in 1D stellar evolution models.

scholarly journals Convective core entrainment in 1D main sequence stellar models

2021 ◽  
Author(s):  
L J A Scott ◽  
R Hirschi ◽  
C Georgy ◽  
W D Arnett ◽  
C Meakin ◽  
...  
Keyword(s):  
Main Sequence ◽  
Mass Dependence ◽  
Bulk Richardson Number ◽  
Chemical Gradient ◽  
Convective Boundary ◽  
Boundary Mixing ◽  
Turbulent Entrainment ◽  
Stellar Convection ◽  
Convective Core ◽  
Solar Metallicity

Abstract 3D hydrodynamics models of deep stellar convection exhibit turbulent entrainment at the convective-radiative boundary which follows the entrainment law, varying with boundary penetrability. We implement the entrainment law in the 1D Geneva stellar evolution code. We then calculate models between 1.5 and 60 M⊙ at solar metallicity (Z = 0.014) and compare them to previous generations of models and observations on the main sequence. The boundary penetrability, quantified by the bulk Richardson number, RiB, varies with mass and to a smaller extent with time. The variation of RiB with mass is due to the mass dependence of typical convective velocities in the core and hence the luminosity of the star. The chemical gradient above the convective core dominates the variation of RiB with time. An entrainment law method can therefore explain the apparent mass dependence of convective boundary mixing through RiB. New models including entrainment can better reproduce the mass dependence of the main sequence width using entrainment law parameters A ∼ 2 × 10−4 and n = 1. We compare these empirically constrained values to the results of 3D hydrodynamics simulations and discuss implications.

scholarly journals Formation of GW190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up and 12C(α, γ)16O rate on the pair-instability black hole mass gap

2020 ◽  
Author(s):  
Guglielmo Costa ◽  
Alessandro Bressan ◽  
Michela Mapelli ◽  
Paola Marigo ◽  
Giuliano Iorio ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Reaction Rate ◽  
Primary Component ◽  
Mass Reduction ◽  
Black Hole Mass ◽  
Core Mass ◽  
The Core ◽  
Mass Gap ◽  
M Stars ◽  
The Impact

Abstract Pair-instability (PI) is expected to open a gap in the mass spectrum of black holes (BHs) between ≈40 − 65 M⊙ and ≈120 M⊙. The existence of the mass gap is currently being challenged by the detection of GW190521, with a primary component mass of $85^{+21}_{-14}$ M⊙. Here, we investigate the main uncertainties on the PI mass gap: the 12C(α, γ)16O reaction rate and the H-rich envelope collapse. With the standard 12C(α, γ)16O rate, the lower edge of the mass gap can be 70 M⊙ if we allow for the collapse of the residual H-rich envelope at metallicity Z ≤ 0.0003. Adopting the uncertainties given by the starlib database, for models computed with the 12C(α, γ)16O rate −1 σ, we find that the PI mass gap ranges between ≈80 M⊙ and ≈150 M⊙. Stars with MZAMS > 110 M⊙ may experience a deep dredge-up episode during the core helium-burning phase, that extracts matter from the core enriching the envelope. As a consequence of the He-core mass reduction, a star with MZAMS = 160 M⊙ may avoid the PI and produce a BH of 150 M⊙. In the −2 σ case, the PI mass gap ranges from 92 M⊙ to 110 M⊙. Finally, in models computed with 12C(α, γ)16O −3 σ, the mass gap is completely removed by the dredge-up effect. The onset of this dredge-up is particularly sensitive to the assumed model for convection and mixing. The combined effect of H-rich envelope collapse and low 12C(α, γ)16O rate can lead to the formation of BHs with masses consistent with the primary component of GW190521.

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