Towards 21st century stellar models: Star clusters, supercomputing and asteroseismology

Campbell, Simon; Constantino, T.; D’Orazi, V.; Stello, Dennis; Christensen‐Dalsgaard, J.; Kuehn, Charles A.; Silva, G.M. De; Arnett, W. David; Lattanzio, John C.; MacLean, B. T.

doi:10.1002/asna.201612373

Cited by 9 publications

(9 citation statements)

References 25 publications

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“…Multidimensional hydrodynamical simulations of convection are key to understanding this mass range. A new theory of convection, such as the 321D theory under development (Arnett et al, 2015;Campbell et al, 2016), would help to constrain the WD/SN boundary .…”

Section: Convectionmentioning

confidence: 99%

Super-AGB Stars and their Role as Electron Capture Supernova Progenitors

Doherty

Gil‐Pons

Siess

et al. 2017

Publ. Astron. Soc. Aust.

161

193

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We review the lives, deaths and nucleosynthetic signatures of intermediate-mass stars in the range ≈6-12 M , which form super-AGB stars near the end of their lives. The critical mass boundaries both between different types of massive white dwarfs (CO, CO-Ne, ONe), and between white dwarfs and supernovae, are examined along with the relative fraction of super-AGB stars that end life either as an ONe white dwarf or as a neutron star (or an ONeFe white dwarf), after undergoing an electron capture supernova event. The contribution of the other potential single-star channel to electroncapture supernovae, that of the failed massive stars, is also discussed. The factors that influence these different final fates and mass limits, such as composition, rotation, the efficiency of convection, the nuclear reaction rates, mass-loss rates, and third dredge-up efficiency, are described. We stress the importance of the binary evolution channels for producing electron-capture supernovae. Recent nucleosynthesis calculations and elemental yield results are discussed and a new set of s-process heavy element yields is presented. The contribution of super-AGB star nucleosynthesis is assessed within a Galactic perspective, and the (super-)AGB scenario is considered in the context of the multiple stellar populations seen in globular clusters. A brief summary of recent works on dust production is included. Last, we conclude with a discussion of the observational constraints and potential future advances for study into these stars on the low mass/high mass star boundary.

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Section: Convectionmentioning

confidence: 99%

Super-AGB Stars and their Role as Electron Capture Supernova Progenitors

Doherty

Gil‐Pons

Siess

et al. 2017

Publ. Astron. Soc. Aust.

161

193

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“…Work is proceeding to improve the physics on the treatment of convection and convective boundaries beyond the Mixing Length Theory (MLT) [see e.g. Arnett et al (2015); Campbell et al (2016); Arnett & Moravveji (2017)]. ii) A better understanding of low-temperature opacities and mass-loss rates is crucial.…”

Section: Future Topics Of Researchmentioning

confidence: 99%

Primordial to extremely metal-poor AGB and Super-AGB stars: White dwarf or supernova progenitors?

Gil‐Pons

Doherty

Gutiérrez

et al. 2018

Publ. Astron. Soc. Aust.

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Getting a better understanding of the evolution and nucleosynthetic yields of the most metal-poor stars (Z 10 −5 ) is critical because they are part of the big picture of the history of the primitive Universe. Yet many of the remaining unknowns of stellar evolution lie in the birth, life, and death of these objects. We review stellar evolution of intermediatemass Z ≤ 10 −5 models existing in the literature, with a particular focus on the problem of their final fates. We emphasize the importance of the mixing episodes between the stellar envelope and the nuclearly processed core, which occur after stars exhaust their central He (second dredge-up and dredge-out episodes). The depth and efficiency of these episodes are critical to determine the mass limits for the formation of electron-capture supernovae (EC-SNe). Our knowledge of these phenomena is not complete because they are strongly affected by the choice of input physics. These uncertainties affect stars in all mass and metallicity ranges. However, difficulties in calibration pose additional challenges in the case of the most metal-poor stars. We also consider the alternative SN I1/2 channel to form supernovae out of the most metal-poor intermediate mass objects. In this case, it is critical to understand the thermally-pulsing AGB evolution until the late stages. Efficient second dredge-up and, later, third dredge-up episodes could be able to pollute stellar envelopes enough for the stars to undergo thermal pulses in a way very similar to that of higher initial Z objects. Inefficient second and/or third dredge-up may leave an almost pristine envelope, unable to sustain strong stellar winds. This may allow the Hexhausted core to grow to the Chandrasekhar mass before the envelope is completely lost, and thus let the star explode as a SN I1/2. After reviewing the information available on these two possible channels for the formation of supernovae, we discuss existing nucleosynthetic yields of stars of metallicity Z ≤ 10 −5 , and present an example of nucleosynthetic calculations for a thermally-pulsing Super-AGB star of Z = 10 −5 . We compare theoretical predictions with observations of the lowest [Fe/H] objects detected. The review closes by discussing current open questions as well as possible fruitful avenues for future research.

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“…Schindler et al (2015) applied atomic diffusion without overshoot to yield monotonic growth in the mass of the convective core (which similarly occurs due to numerical diffusion in MONSTAR models without explicit overshoot and an insufficiently resolved mesh; see e.g. the upper panel of Figure 1 in Campbell et al 2016). VandenBerg et al (2016) and Denissenkov et al (2017) produce a similar structure by choosing appropriate parameters for the mixing scheme described by Equation 1: they use a small value for the parameter fOS, which is then reduced further late in CHeB; they also measure D0 from close to the convective boundary and replace it with a fraction of the thermal diffusivity K when D0 < K.…”

Section: Recent Progress In Modellingmentioning

confidence: 99%

The treatment of mixing in core helium-burning models – III. Suppressing core breathing pulses with a new constraint on overshoot

Constantino

Campbell

Lattanzio

2017

Monthly Notices of the Royal Astronomical Society

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Theoretical predictions for the core helium burning phase of stellar evolution are highly sensitive to the uncertain treatment of mixing at convective boundaries. In the last few years, interest in constraining the uncertain structure of their deep interiors has been renewed by insights from asteroseismology. Recently, Spruit (2015) proposed a limit for the rate of growth of helium-burning convective cores based on the higher buoyancy of material ingested from outside the convective core. In this paper we test the implications of such a limit for stellar models with a range of initial mass and metallicity. We find that the constraint on mixing beyond the Schwarzschild boundary has a significant effect on the evolution late in core helium burning, when core breathing pulses occur and the ingestion rate of helium is fastest. Ordinarily, core breathing pulses prolong the core helium burning lifetime to such an extent that models are at odds with observations of globular cluster populations. Across a wide range of initial stellar masses (0.83 ≤ M/M ⊙ ≤ 5), applying the Spruit constraint reduces the core helium burning lifetime because core breathing pulses are either avoided or their number and severity reduced. The constraint suggested by Spruit therefore helps to resolve significant discrepancies between observations and theoretical predictions. Specifically, we find improved agreement for R 2 , the observed ratio of asymptotic giant branch to horizontal branch stars in globular clusters; the luminosity difference between these two groups; and in asteroseismology, the mixed-mode period spacing detected in red clump stars in the Kepler field.

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Towards 21st century stellar models: Star clusters, supercomputing and asteroseismology

Cited by 9 publications

References 25 publications

Super-AGB Stars and their Role as Electron Capture Supernova Progenitors

Super-AGB Stars and their Role as Electron Capture Supernova Progenitors

Primordial to extremely metal-poor AGB and Super-AGB stars: White dwarf or supernova progenitors?

The treatment of mixing in core helium-burning models – III. Suppressing core breathing pulses with a new constraint on overshoot

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