The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars

Suda, Takuma; Yamada, Shimako; Fujimoto, Masayuki Y.

doi:10.7566/jpscp.14.010901

Cited by 2 publications

(2 citation statements)

References 16 publications

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“…CEMP-no stars are traditionally assumed to have formed from a previous generation of massive stars from which they inherited their chemical peculiarities, but doubts have been cast on this hypothesis. Considering the continuity of the [Ba/C] distribution as a function of [Fe/H] in CEMP-s and CEMPno stars, Abate et al (2015b) and Suda et al (2017a) suggested that CEMP-s and (some) CEMP-no objects might have a common origin involving binarity. Observational studies that analysed the binary fraction of different subclasses of CEMP stars support this hypothesis (Starkenburg et al, 2014;Hansen et al, 2016a).…”

Section: Present Open Questionsmentioning

confidence: 99%

“…The heavier species synthesised would then act as seeds to form s-process elements. Once transported to the surface by third dredge-up, these stars are expected to display Pb and Bi enhancements [see also Suda, Yamada, & Fujimoto (2017a)]. Cruz et al (2013) also computed and analysed s-process nucleosynthesis in 1 M stars between primordial and Z = 10 −7 .…”

Section: Nucleosynthesis In Emp Stars Undergoing 'Normal' Thermally Pmentioning

confidence: 99%

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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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Section: Present Open Questionsmentioning

confidence: 99%

Section: Nucleosynthesis In Emp Stars Undergoing 'Normal' Thermally Pmentioning

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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Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

Komiya

Suda

Yamada

et al. 2020

ApJ

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Mixing and fallback models in faint supernova models are supposed to reproduce the abundance patterns of observed carbon-enhanced metal-poor (CEMP) stars in the Galactic halo. A fine tuning of the model parameters for individual stars is required to reproduce the observed ratios of carbon to iron. We focus on extremely metal-poor stars formed out of the ejecta from the mixing and fallback models using a chemical evolution model. Our chemical evolution models take into account the contribution of individual stars to chemical enrichment in host halos together with their evolution in the context of the hierarchical clustering. Parametrized models of mixing and fallback models for Pop. III faint supernovae are implemented in the chemical evolution models with merger trees to reproduce the observed CEMP stars. A variety of choices for model parameters on star formation and metal-pollution by faint supernovae is unable to reproduce the observed stars with [Fe/H] −4 and [C/H] −2, which are the majority of CEMP stars among the lowest metallicity stars. Only possible solution is to form stars from small ejecta mass, which produces an inconsistent metallicity distribution function. We conclude that not all the CEMP stars are explicable by the mixing and fallback models. We also tested the contribution of binary mass transfers from AGB stars that are also supposed to reproduce the abundances of known CEMP stars. This model reasonably reproduces the distribution of carbon and iron abundances simultaneously only if we assume that long-period binaries are favored at [Fe/H] −3.5.

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The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars

Cited by 2 publications

References 16 publications

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

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

Are Faint Supernovae Responsible for Carbon-enhanced Metal-poor Stars?

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