F

Herwig, Heinz

doi:10.1007/978-3-322-80251-4_6

Cited by 189 publications

(355 citation statements)

References 3 publications

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“…Smith and Lambert, 1988) C-stars lose mass through strong, cool winds rich in dust; hence, they can pollute the interstellar medium (ISM) with C-based grains, carrying the signature of the nucleosynthesis processes that occurred in their stellar interior. Reviews of these phenomena can be found, e.g., in Iben and Renzini (1983), Busso et al (1999), Herwig (2005), Avila et al (2012) and Karakas and Lattanzio (2014).…”

Section: Introductionmentioning

confidence: 99%

s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains

Palmerini

Trippella

Busso

et al. 2018

Geochimica et Cosmochimica Acta

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In the past years the observational evidence that s-process elements from Sr to Pb are produced by stars ascending the socalled Asymptotic Giant Branch (or ''AGB") could not be explained by self-consistent models, forcing researchers to extensive parameterizations. The crucial point is to understand how protons can be injected from the envelope into the He-rich layers, yielding the formation of 13 C and then the activation of the 13 Cða; nÞ 16 O reaction. Only recently, attempts to solve this problem started to consider quantitatively physically-based mixing mechanisms. Among them, MHD processes in the plasma were suggested to yield mass transport through magnetic buoyancy. In this framework, we compare results of nucleosynthesis models for Low Mass AGB Stars (M K 3M ), developed from the MHD scenario, with the record of isotopic abundance ratios of s-elements in presolar SiC grains, which were shown to offer precise constraints on the 13 C reservoir. We find that n-captures driven by magnetically-induced mixing can indeed account for the SiC data quite well and that this is due to the fact that our 13 C distribution fulfils the above constraints rather accurately. We suggest that similar tests should be now performed using different physical models for mixing. Such comparisons would indeed improve decisively our understanding of the formation of the neutron source.

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Section: Introductionmentioning

confidence: 99%

s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains

Palmerini

Trippella

Busso

et al. 2018

Geochimica et Cosmochimica Acta

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“…Moreover, possible physical mechanisms for producing a 13 C pocket of the suitable mass and with the appropriate abundance distribution have been extensively investigated by different authors, in order to find a secure basis for s-process nucleosynthesis in stars. Recent mechanisms suggested as the cause of proton penetration are: i) chemical diffusion during the interpulse phase; ii) hydrodynamical effects induced by convective overshooting [5,8]; iii) gravitational waves [6]; iv) magnetic fields generating buoyancy [14,20]. As a consequence of H penetration, protons can interact with 12 C producing the 13 C reservoir.…”

Section: The 13 C-pocket Formationmentioning

confidence: 99%

Does the main component of the s-process in AGB stars constrain the neutron source in the 13C-pocket?

Trippella¹

2015

Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII)

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The 13 C(α, n) 16 O reaction is considered as the main responsible for the production of the sprocess main component in low-mass AGB stars. Its activation requires a physical mechanism to ingest protons in the He-rich region forming a 13 C reservoir, or pocket. This was typically assumed to involve a small mass (≤ 10 −3 M ) [7], but recent observations in several astrophysical sites showed enhancements of s-element abundances with respect to the Sun suggesting a more effective s-process nucleosynthesis. This requires a more extended 13 C pocket covering, in mass (≥ 4 × 10 −3 M ), most of the He-rich layers. Recently, we suggested that magnetic buoyancy could promote forced mixing [14,20] to produce a 13 C reservoir larger than assumed so far. Here we investigate if the solar composition of neutron rich elements, from Sr to Bi, can constrain the 13 C-pocket extension. Stellar models at a fixed metallicity, based on a large 13 C reservoir reproduce the distribution of s-only elements within the uncertainty of 10%, also fulfilling C-star luminosity observations. Assuming this new scenario, a large production of nuclei below A = 90 is expected, so that 86, 87 Sr may be fully synthesized by AGB stars, while 88 Sr, 89 Y and 94 Zr are contributed more efficiently than before.

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“…A textbook on AGB stars is now available and covers the interior evolution and the atmosphere, circumstellar and other observational properties (Habing & Olofsson, 2004). Another recent review (Herwig, 2005) covers current developements in more detail.…”

Section: Introductionmentioning

confidence: 99%

AGB stars evolution & nucleosynthesis

Herwig¹

2010

Proceedings of International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX — PoS(NIC-IX)

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Asymptotic Giant Branch stars are the main nuclear production phase of low-and intermediate mass stars. The double-shell burning of He and H around the electron degenerate core drives a rich pattern of nucleosynthesis, including the slow neutron capture process, as well as the formation of neutron rich isotopes. This nucleosynthesis is now observationally accessible in extremely metal poor stars, in particular the carbon enhanced s-process rich stars in binaries. The most common approach to model AGB star evolution and nucleosynthesis is the one-dimensional, spherically symmetric stellar evolution approximation. The input physics (mass loss, convective and nonconvective mixing, nucleosynthesis) and their uncertainties are discussed. More recently, hydrodynamic simulations of He-shell flash convection are becoming available, providing the means for a detailed analysis of some of the uncertain aspects of one-dimensional models. The differences between stellar interior convection and shallow surface convection is discussed. We also report on new studies that investigate the sensitivity of mixing and element production to nuclear reaction rates.

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F

Cited by 189 publications

References 3 publications

s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains

s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains

Does the main component of the s-process in AGB stars constrain the neutron source in the 13C-pocket?

AGB stars evolution & nucleosynthesis

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