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 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 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 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 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 Helium, [Fe/H] Abundances and the HR (Log TEFF, MBol) Diagram With Hipparcos Data of The Four Nearest Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe

1998 ◽  
Vol 11 (1) ◽  
pp. 565-565
Author(s):  
G. Cayrel de Strobel ◽  
R. Cayrel ◽  
Y. Lebreton
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Spectroscopic Analyses ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
The Moment ◽  
The One ◽  
Best Fit

After having studied in great detail the observational HR diagram (log Teff, Mbol) composed by 40 main sequence stars of the Hyades (Perryman et al.,1997, A&A., in press), we have tried to apply the same method to the observational main sequences of the three next nearest open clusters: Coma Berenices, the Pleiades, and Praesepe. This method consists in comparing the observational main sequence of the clusters with a grid of theoretical ZAMSs. The stars composing the observational main sequences had to have reliable absolute bolometric magnitudes, coming all from individual Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. If we assume, following the work by Fernandez et al. (1996, A&A,311,127), that the mixing-lenth parameter is solar, the position of a theoretical ZAMS, in the (log Teff, Mbol) plane, computed with given input physics, only depends on two free parameters: the He content Y by mass, and the metallicity Z by mass. If effective temperature and metallicity of the constituting stars of the 4 clusters are previously known by means of detailed analyses, one can deduce their helium abundances by means of an appropriate grid of theoretical ZAMS’s. The comparison between the empirical (log Teff, Mbol) main sequence of the Hyades and the computed ZAMS corresponding to the observed metallicity Z of the Hyades (Z= 0.0240 ± 0.0085) gives a He abundance for the Hyades, Y= 0.26 ± 0.02. Our interpretation, concerning the observational position of the main sequence of the three nearest clusters after the Hyades, is still under way and appears to be greatly more difficult than for the Hyades. For the moment we can say that: ‒ The 15 dwarfs analysed in detailed in Coma have a solar metallicity: [Fe/H] = -0.05 ± 0.06. However, their observational main sequence fit better with the Hyades ZAMS. ‒ The mean metallicity of 13 Pleiades dwarfs analysed in detail is solar. A metal deficient and He normal ZAMS would fit better. But, a warning for absorption in the Pleiades has to be recalled. ‒ The upper main sequence of Praesepe, (the more distant cluster: 180 pc) composed by 11 stars, analysed in detail, is the one which has the best fit with the Hyades ZAMS. The deduced ‘turnoff age’ of the cluster is slightly higher than that of the Hyades: 0.8 Gyr instead of 0.63 Gyr.

scholarly journals Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

2019 ◽  
Vol 624 ◽  
pp. A137 ◽  
Author(s):  
L. Haemmerlé ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Stellar Clusters ◽  
Solar Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

scholarly journals Convective boundary mixing in a post-He core burning massive star model

2018 ◽  
Vol 484 (3) ◽  
pp. 3921-3934 ◽  
Author(s):  
A Davis ◽  
S Jones ◽  
F Herwig
Keyword(s):  
Massive Star ◽  
Star Model ◽  
Convective Boundary ◽  
Boundary Mixing

scholarly journals The effects of Rotation on Wolf–Rayet Stars and on the Production of Primary Nitrogen by Intermediate Mass Stars

2004 ◽  
Vol 215 ◽  
pp. 579-588 ◽  
Author(s):  
Georges Meynet ◽  
Max Pettini
Keyword(s):  
Star Formation ◽  
Time Delay ◽  
Main Sequence ◽  
Massive Stars ◽  
Sequence Evolution ◽  
Stellar Rotation ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Solar Metallicity ◽  
Effects Of Rotation

We use the rotating stellar models described in the paper by A. Maeder & G. Meynet in this volume to consider the effects of rotation on the evolution of the most massive stars into and during the Wolf–Rayet phase, and on the post-Main Sequence evolution of intermediate mass stars. The two main results of this discussion are the following. First, we show that rotating models are able to account for the observed properties of the Wolf–Rayet stellar populations at solar metallicity. Second, at low metallicities, the inclusion of stellar rotation in the calculation of chemical yields can lead to a longer time delay between the release of oxygen and nitrogen into the interstellar medium following an episode of star formation, since stars of lower masses (compared to non-rotating models) can synthesize primary N. Qualitatively, such an effect may be required to explain the relative abundances of N and O in extragalactic metal–poor environments, particularly at high redshifts.

scholarly journals The Delta Scuti Star GX Pegasi: A Theoretical Investigation of its Power Spectrum

1993 ◽  
Vol 134 ◽  
pp. 181-183
Author(s):  
E. Michel ◽  
M. J. Goupil ◽  
Y. Lebreton ◽  
A. Baglin
Keyword(s):  
Power Spectrum ◽  
Theoretical Investigation ◽  
Main Sequence ◽  
Main Sequence Star ◽  
Mode Identification ◽  
Star Models ◽  
Convective Core ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti

Target of a STEPHI multisite campaign, the Delta Scuti star GX Pegasi has been found to oscillate with at least five simultaneous, close frequencies (table I).Mode identification together with informations about the star that such an identification can provide are outlined below (see also Michel et al, 1992b).The mode identification is carried out by means of a comparison between the observed frequencies and the adiabatic frequencies of models appropriate to this star. Models that match GX Peg’s position in a Hertzsprung-Russell diagram have masses in the range 1.9 – M⊙. When included, convective core overshoot is handled as in Maeder and Meynet (1989). According to these models, GX Peg is a rather evolved, main sequence star.

scholarly journals 35. Commission De La Constitution Des Etoiles

1950 ◽  
Vol 7 ◽  
pp. 367-368
Author(s):  
M. H. N. Russell
Keyword(s):  
Main Sequence ◽  
Successive Approximations ◽  
Atomic Composition ◽  
The Past ◽  
Convective Core ◽  
Internal Constitution ◽  
The Mean ◽  
Present Summary ◽  
Mean Molecular Weight ◽  
Uniform Composition

The study of the internal constitution of the stars has advanced rapidly in the past few years, especially for those of the main sequence. The present summary is necessarily brief.For a star of uniform composition, whose interior is in radiative equilibrium, with or without a convective core, the constitution can be completely determined by successive approximations by quadratures, if there are given(a)the atomic composition(b)the equation of state, defining the mean molecular weight μ(c)the equation defining the opacity for the outflowing radiation(d)the equation defining the rate of liberation of energy per gram.

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