Evolution and nucleosynthesis of helium-rich asymptotic giant branch models

Shingles, Luke J.; Doherty, Carolyn; Karakas, Amanda I.; Stancliffe, Richard J.; Lattanzio, John C.; Lugaro, Maria

doi:10.1093/mnras/stv1489

Cited by 24 publications

(47 citation statements)

References 118 publications

(145 reference statements)

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“…Most heavy elements, X, are only moderately overabundant, with 0<[X/Fe]<1. We compare this pattern with six sets of low-metallicity ([Fe/H]=−1.4) AGB nucleosynthesis yields, with Y=0.24, taken from and Shingles et al (2015). Several example fits are shown.…”

Section: Comparison With Agb Nucleosynthesis Predictionsmentioning

confidence: 99%

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THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

Roederer

Karakas

Pignatari

et al. 2016

ApJ

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105

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We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metalpoor ( We analyze an archival near-ultraviolet spectrum of HD94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64species of 56elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s-and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutroncapture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the iprocess appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the iprocess may have been common in the early Galaxy.

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Section: Comparison With Agb Nucleosynthesis Predictionsmentioning

confidence: 99%

“…We use the low-metallicity AGB evolution and nucleosynthesis models from and Shingles et al (2015). These models were calculated with an initial metallicity of Z=0.0006 ([Fe/H] =−1.4), which is close to the derived metallicity of HD94028.…”

Section: Agb Modelsmentioning

confidence: 99%

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

Roederer

Karakas

Pignatari

et al. 2016

ApJ

Self Cite

105

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“…The models of Gallino et al (1998) (and follow-up studies by, e.g., Bisterzo et al 2010Bisterzo et al , 2011Liu et al 2015) are calculated by including some 13 C in the intershell and exploring a large variety of extents and abundance profiles. The models of, e.g., Goriely & Mowlavi (2000); Lugaro et al (2012); Fishlock et al (2014); Shingles et al (2015); instead are calculated including a PMZ by means of an artificial mixing profile, driving the mixing of protons that subsequently produce a 13 C abundance profile. The mixing is modelled using an exponential function where the exponent is a linear function of the mass ("standard" case, see details in Sec.…”

Section: Current Models For the Formation Of 13 C Pocketsmentioning

confidence: 99%

Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

Buntain

Doherty

Lugaro

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The production of the elements heavier than iron via slow neutron captures (the s process) is a main feature of the contribution of asymptotic giant branch (AGB) stars of low mass (< 5 Msun) to the chemistry of the cosmos. However, our understanding of the main neutron source, the 13 C(α,n) 16 O reaction, is still incomplete. It is commonly assumed that in AGB stars mixing beyond convective borders drives the formation of 13 C pockets. However, there is no agreement on the nature of such mixing and free parameters are present. By means of a parametric model we investigate the impact of different mixing functions on the final s-process abundances in low-mass AGB models. Typically, changing the shape of the mixing function or the mass extent of the region affected by the mixing produce the same results. Variations in the relative abundance distribution of the three s-process peaks (Sr, Ba, and Pb) are generally within +/-0.2 dex, similar to the observational error bars. We conclude that other stellar uncertainties -the effect of rotation and of overshoot into the C-O core -play a more important role than the details of the mixing function. The exception is at low metallicity, where the Pb abundance is significantly affected. In relation to the composition observed in stardust SiC grains from AGB stars, the models are relatively close to the data only when assuming the most extreme variation in the mixing profile.

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“…We note that CONe cores are found over a large variety of metallicities and also for a range of helium enrichments (Shingles et al 2015). In any case, a narrow mass range would allow us to explain at most a few percent of the observed SNIa (Meng & Podsiadlowski 2014).…”

Section: Introductionmentioning

confidence: 76%

Explosion of white dwarfs harboring hybrid CONe cores

Bravo

Gil‐Pons

Gutiérrez

et al. 2016

A&A

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Recently, it has been found that off-center carbon burning in a subset of intermediate-mass stars does not propagate all the way to the center, resulting in a class of hybrid CONe cores. The implications of a significant presence of carbon in the resulting massive degenerate cores have not been thoroughly explored so far. Here, we consider the possibility that stars hosting these hybrid CONe cores might belong to a close binary system and, eventually, become white dwarfs accreting from a nondegenerate companion at rates leading to a supernova explosion. We computed the hydrodynamical phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid cores, assuming that the explosion starts at the center; this explosion occurs either as a detonation, as may be expected in some degenerate merging scenarios, or as a deflagration that afterward transitions into a delayed detonation. We assume these hybrid cores are made of a central CO volume, of mass M CO , surrounded by an ONe shell. We show that, in the case of a pure detonation, a medium-sized carbon-rich region, M CO (<0.4 M ), results in the ejection of a small fraction of the mantle while leaving a massive bound remnant. Part of this remnant is made of the products of the detonation, that is, Fe-group nuclei, but they are buried in its inner regions unless convection is activated during the ensuing cooling and shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed detonations do not leave remnants other than for the minimum M CO we explored of M CO = 0.2 M , and even in this case the remnant is as small as 0.13 M . The ejecta produced by these delayed detonations are characterized by slightly smaller masses of 56 Ni and substantially smaller kinetic energies than the ejecta obtained for a delayed detonation of a "normal" CO white dwarf. The optical emission expected from these explosions most likely do not match the observational properties of typical Type Ia supernovae, although they make interesting candidates for the subluminous class of SN2002cx-like or SNIax.

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Evolution and nucleosynthesis of helium-rich asymptotic giant branch models

Cited by 24 publications

References 118 publications

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

Explosion of white dwarfs harboring hybrid CONe cores

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