THE s -PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS
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We present models for the slow neutron-capture process ( s -process) in asymptotic giant branch stars of metallicity [Fe/H] = −2.3 and masses 0.9–6 M ☉ . We encountered different regimes of neutron-capture nucleosynthesis listed here increasing in importance as the stellar mass decreases: the 22 Ne(α, n ) 25 Mg reaction activated during the thermal pulses (TPs), the 13 C(α, n ) 16 O reaction activated in radiative conditions during the interpulse periods, and the 13 C(α, n ) 16 O reaction activated during the TPs, also as a result of mild proton-ingestion episodes. The models where the 13 C burns radiatively (masses ≃2 M ☉ ) produce an overall good match to carbon-enhanced metal-poor (CEMP) stars showing s -process enhancements (CEMP- s ), except they produce too much Na and F. On the other hand, none of our models can provide a match to the composition of CEMP stars also showing rapid -process enhancements (CEMP- s / r ). The models fail to reproduce the observed Eu abundances, and they also fail to reproduce the correlation between the Eu and Ba abundances. They also cannot match the ratio of heavy-to-light s -process elements observed in many CEMP- s / r stars, which can be more than 10 times higher than in the solar system. To explain the composition of CEMP- s / r stars we need to invoke the existence of a different " s / r " neutron-capture process either with features in between the s - and the r -processes, or generated by superpositions of different neutron-capture processes in the same astrophysical site or in sites linked to each other—for example, in multiple stellar systems.
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Calculations of low-metallicity (Z ≤ 0.001) intermediate-mass stars suggest that C-star formation will occur before HBB ceases.
“calculations of low-metallicity ( Z ≤ 0 . 001) intermediate-mass stars suggest that C-star formation will occur before HBB ceases”
From The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014) · cites this paper as Lugaro et al. 2012
At Z = 0.0001, proton ingestion (Regime 4) dominates the s-process abundance predictions at the lowest masses (M ≤ 1 M⊙) when no (or small) 13C pockets are present.
“At the metallicity considered in that study ( Z = 0 . 0001) proton ingestion (Regime 4) dominates the s -process abundance predictions at the lowest masses ( M ≤ 1 M ⊙ at Z = 0 . 0001) when no (or small) 13 Cpocketsarepresent.”
From The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014) · cites this paper as Lugaro et al. 2012
Such low observed 12C/13C ratios are difficult to reconcile with standard AGB nucleosynthesis models, which produce very high 12C/13C ratios (>10^3) at low metallicity.
“Such low observed ratios are difficult to reconcile with standard AGB nucleosynthesis models, which produce very high 12 C/ 13 C ratios ( > 10 3 ) at low metallicity (e.g., Karakas 2010; Cristallo et al. 2011; Lugaro et al. 2012).”
From The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014) · cites this paper as Lugaro et al. 2012
Regime 3 is possibly a common occurrence during the first few thermal pulses for all low-mass AGB stars of ≲2 M⊙, regardless of Z.
“Hence Regime 3, where all or most of the 13 Cis burnt under convective conditions during the next thermal pulse is possibly a common occurrence during the first few thermal pulses for all low-mass AGB stars of ≲ 2 M ⊙ , regardless of Z (see also Cristallo et al. 2009; Lugaro et al. 2012).”
From The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014) · cites this paper as Lugaro et al. 2012
Lugaro et al. (2012) present tables of stellar abundance predictions as a function of thermal pulse number from models from 0.9 to 6 M⊙ for only one metallicity (Z = 0.0001 or [Fe/H] = -2.3).
“Lugaro et al. (2012) present tables of stellar abundance predictions as a function of thermal pulse number from models from 0.9 to 6 M ⊙ for only one metallicity ( Z = 0 . 0001 or [ Fe/H ] =-2 . 3).”
From The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014) · cites this paper as Lugaro et al. (2012)
Cites
Two stellar components in the halo of the Milky Way
Carollo, D., Beers, T. C., Lee, Y. S., Chiba, M., Norris, J. E., Wilhelm, R., Sivarani, T., Marsteller, B., Munn, J. A., Bailer-Jones, C. A. L., et al. (2007) · Nature · doi:10.1038/nature06460 · Cited by 626 · see citing works
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The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars
Karakas, A. I., & Lattanzio, J. C. (2014) · Publications of the Astronomical Society of Australia · doi:10.1017/pasa.2014.21 · Cited by 735 · see citing works
“2M⊙, regardless of Z (see also Cristallo et al. 2009; Lugaro et al. 2012).”
BackgroundMethodResultInfluentialSelf-citation
- Authors
- Lugaro, M., Karakas, A. I., Stancliffe, R. J., & Rijs, C.
- Affiliations
- Monash University (AU)
- Mount Stromlo Observatory (AU)
- Venue
- The Astrophysical Journal
- Publisher
- American Astronomical Society
- Published
- 2012-02-07
- Volume
- 747
- Issue
- 1
- Pages
- 2
- ISSN
- 0004-637X (ISSN-L)
- 1538-4357
- OpenAlex
- W2039567845
- Cited by
- 271
- References
- 1
- Citations by year
- 2026: 10 · 2025: 16 · 2024: 14 · 2023: 13 · 2022: 15 · 2021: 16 · 2020: 18 · 2019: 20 · 2018: 17 · 2017: 18 · 2016: 21 · 2015: 20 · 2014: 25 · 2013: 29 · 2012: 17
- FWCI
- 15.94
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- The Astrophysical Journal (publishedVersion)
- arXiv (Cornell University) (submittedVersion)
- ANU Open Research (Australian National University) (submittedVersion)
- arXiv (Cornell University)
- Funders
- National Cancer Institute
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
- Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Nuclear physics research studies
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Gamma-ray bursts and supernovae
- Keywords
- s-process nucleosynthesis, asymptotic giant branch stars, low metallicity, carbon-enhanced metal-poor stars, 13C(α,n)16O reaction, 22Ne(α,n)25Mg reaction, thermal pulses, europium abundance, neutron-capture nucleosynthesis, stellar mass dependence
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