The evolution of low-metallicity asymptotic giant branch stars and the formation of carbon-enhanced metal-poor stars

Lau, Herbert H. B.; Stancliffe, Richard J.; Tout, Christopher A.

doi:10.1111/j.1365-2966.2009.14772.x

Cited by 66 publications

(87 citation statements)

References 41 publications

(68 reference statements)

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“…The occurrence of such a mixing phenomenon depends on the initial stellar mass and metallicity: the lower the mass and the metallicity, the higher the probability for a PIE to occur. At extremely low metallicities ([Fe/H]<-3), a PIE can be found during the off-center He-burning flash, while for larger Z (-3<[Fe/H]<-2) it may occur at the first fully developed TP (Hollowell et al 1990;Fujimoto et al 2000;Iwamoto et al 2004;Campbell & Lattanzio 2008;Lau et al 2009). 3D hydrodynamical simulations confirm this peculiarity, which characterizes very metal-poor models (Woodward et al 2008).…”

Section: The Cemp Casementioning

confidence: 99%

Constraints of the Physics of Low-Mass Agb Stars From Ch and Cemp Stars

Cristallo

Karinkuzhi

Goswami

et al. 2016

ApJ

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We analyze a set of published elemental abundances from a sample of CH stars which are based on high resolution spectral analysis of ELODIE and SUBARU/HDS spectra. All the elemental abundances were derived from local thermodynamic equilibrium analysis using model atmospheres, and thus, they represent the largest homogeneous abundance data available for CH stars up to date. For this reason, we can use the set to constrain the physics and the nucleosynthesis occurring in low mass AGB stars. CH stars have been polluted in the past from an already extinct AGB companion and thus show s-process enriched surfaces. We discuss the effects induced on the -2 -surface AGB s-process distributions by different prescriptions for convection and rotation. Our reference theoretical FRUITY set fits only part of the observations. Moreover, the s-process observational spread for a fixed metallicity cannot be reproduced. At [Fe/H]>-1, a good fit is found when rotation and a different treatment of the inner border of the convective envelope are simultaneously taken into account. In order to increase the statistics at low metallicities, we include in our analysis a selected number of CEMP stars and, therefore, we compute additional AGB models down to [Fe/H]=-2.85. Our theoretical models are unable to attain the large [hs/ls] ratios characterizing the surfaces of those objects. We speculate on the reasons for such a discrepancy, discussing the possibility that the observed distribution is a result of a proton mixing episode leading to a very high neutron density (the so-called i-process).

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Section: The Cemp Casementioning

confidence: 99%

Constraints of the Physics of Low-Mass Agb Stars From Ch and Cemp Stars

Cristallo

Karinkuzhi

Goswami

et al. 2016

ApJ

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“…Many evolution codes experience numerical problems that could be related to this instability. The MONSTAR code (Campbell & Lattanzio 2008) and the STAREVOL code (Siess 2007(Siess , 2010 and the STARS code (Stancliffe & Jeffery 2007;Lau et al 2009) have convergence problems during the late massive AGB or super-AGB evolution.…”

Section: Physical Description Of the Instabilitymentioning

confidence: 99%

The end of super AGB and massive AGB stars

Lau

Gil‐Pons

Doherty

et al. 2012

A&A

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Context. The literature is rich in analysis and results related to thermally pulsing-asymptotic giant branch (TP-AGB) stars, but the problem of the instabilities that arise and cause the divergence of models during the late stages of their evolution is rarely addressed. Aims. We investigate the physical conditions, causes and consequences of the interruption in the calculations of massive AGB stars in the late thermally-pulsing AGB phase. Methods. We have thoroughly analysed the physical structure of a solar metallicity 8.5 M star and described the physical conditions at the base of the convective envelope (BCE) just prior to divergence. Results. We find that the local opacity maximum caused by M-shell electrons of Fe-group elements lead to the accumulation of an energy excess, to the departure of thermal equilibrium conditions at the base of the convective envelope and, eventually, to the divergence of the computed models. For the 8.5 M case we present in this work the divergence occurs when the envelope mass is about 2 M . The remaining envelope masses range between somewhat less than 1 and more than 2 M for stars with initial masses between 7 and 10 M and, therefore, our results are relevant for the evolution and yields of super-AGB stars. If the envelope is ejected as a consequence of the instability we are considering, the occurrence of electron-capture supernovae would be avoided at solar metallicity.

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“…for the CEMPno category, Placco et al 2016;Yoon et al 2016;Choplin et al 2017). For CEMP-s stars, the main formation scenario is the asymptotic giant branch (AGB) scenario, suggesting that a more massive AGB companion has fed the secondary in carbon and s-elements during a mass transfer (or wind mass transfer) episode (Stancliffe & Glebbeek 2008;Lau et al 2009;Bisterzo et al 2010;Lugaro et al 2012;Abate et al 2013Abate et al , 2015bHollek et al 2015). Interestingly, it has been shown by Matrozis & Stancliffe (2017) that rotational mixing in the CEMP-s stars can severely inhibit atomic diffusion.…”

Section: Introductionmentioning

confidence: 99%

Are some CEMP-s stars the daughters of spinstars?

Choplin

Hirschi

Meynet

et al. 2017

A&A

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Carbon-enhanced metal-poor (CEMP)-s stars are long-lived low-mass stars with a very low iron content as well as overabundances of carbon and s-elements. Their peculiar chemical pattern is often explained by pollution from an asymptotic giant branch (AGB) star companion. Recent observations have shown that most CEMP-s stars are in binary systems, providing support to the AGB companion scenario. A few CEMP-s stars, however, appear to be single. We inspect four apparently single CEMP-s stars and discuss the possibility that they formed from the ejecta of a previous-generation massive star, referred to as the "source" star. In order to investigate this scenario, we computed low-metallicity massive-star models with and without rotation and including complete s-process nucleosynthesis. We find that non-rotating source stars cannot explain the observed abundance of any of the four CEMP-s stars. Three out of the four CEMP-s stars can be explained by a 25 M source star with v ini ∼ 500 km s −1 (spinstar). The fourth CEMP-s star has a high Pb abundance that cannot be explained by any of the models we computed. Since spinstars and AGB predict different ranges of [O/Fe] and [ls/hs], these ratios could be an interesting way to further test these two scenarios.

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The evolution of low-metallicity asymptotic giant branch stars and the formation of carbon-enhanced metal-poor stars

Cited by 66 publications

References 41 publications

Constraints of the Physics of Low-Mass Agb Stars From Ch and Cemp Stars

Constraints of the Physics of Low-Mass Agb Stars From Ch and Cemp Stars

The end of super AGB and massive AGB stars

Are some CEMP-s stars the daughters of spinstars?

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