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The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
Solar and Stellar Astrophysics · Submitted 21 Sep 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Our models can synthesise heavy elements up to Pb without any parametrized extra mixing process such as overshoot or inclusion of a $^{13}$C-pocket.
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The abstract, sentence by sentence
Alongside the slow (s) and rapid (r) neutron capture processes, an intermediate neutron capture process (i-process) is thought to exist. It happens when protons are mixed in a convective helium-burning zone, and is referred to as proton ingestion event (PIE). A possible astrophysical site is the asymptotic giant branch (AGB) phase of low-mass low-metallicity stars. We provide i-process yields of a grid of AGB stars experiencing PIEs. We computed 12 models with initial masses of 1, 2, and 3 $M_{\odot}$ and metallicities of [Fe/H] $=-3.0$, $-2.5$ $-2.3,$ and $-2.0, $ with the stellar evolution code STAREVOL. We used a nuclear network of 1160 species at maximum, coupled to the chemical transport equations. These simulations do not include any extra mixing process. Proton ingestion takes place in six out of our 12 AGB models. These models experience i-process nucleosynthesis characterized by neutron densities of $\simeq 10^{14} -10^{15}$ cm$^{-3}$. Depending on the PIE properties two different evolution paths follow: either the stellar envelope is quickly lost and no more thermal pulses develop or the AGB phase resumes with additional thermal pulses. This behaviour critically depends on the pulse number when the PIE occurs, the mass of the ingested protons, and the extent to which the pulse material is diluted in the convective envelope. The surface enrichment after a PIE is a robust feature of our models and it persists under various convective assumptions. Our models can synthesise heavy elements up to Pb without any parametrized extra mixing process such as overshoot or inclusion of a $^{13}$C-pocket. Nevertheless, it remains to be explored how the i-process depends on mixing processes, such as overshoot, thermohaline, or rotation.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Alongside the slow (s) and rapid (r) neutron capture processes, an intermediate neutron capture process (i-process) is thought to exist. | background 1.00 | 0.04 | 0.03 | hedged possibility 0.88 |
| s1 | It happens when protons are mixed in a convective helium-burning zone, and is referred to as proton ingestion event (PIE). | background 1.00 | 0.07 | 0.03 | asserted 1.00 |
| s2 | A possible astrophysical site is the asymptotic giant branch (AGB) phase of low-mass low-metallicity stars. | background 0.99 | 0.07 | 0.04 | hedged possibility 1.00 |
| s3 | We provide i-process yields of a grid of AGB stars experiencing PIEs. | contribution 1.00 | 0.96 | 0.10 | asserted 0.99 |
| s4 | We computed 12 models with initial masses of 1, 2, and 3 $M_{\odot}$ and metallicities of [Fe/H] $=-3.0$, $-2.5$ $-2.3,$ and $-2.0, $ with the stellar evolution code STAREVOL. | method 0.95 | 0.97 | 0.04 | asserted 0.99 |
| s5 | We used a nuclear network of 1160 species at maximum, coupled to the chemical transport equations. | method 1.00 | 0.93 | 0.02 | asserted 1.00 |
| s6 | These simulations do not include any extra mixing process. | method 0.70 | 0.84 | 0.04 | asserted 1.00 |
| s7 | Proton ingestion takes place in six out of our 12 AGB models. | result 1.00 | 0.96 | 0.07 | asserted 1.00 |
| s8 | These models experience i-process nucleosynthesis characterized by neutron densities of $\simeq 10^{14} -10^{15}$ cm$^{-3}$. | result 1.00 | 0.93 | 0.17 | asserted 1.00 |
| s9 | Depending on the PIE properties two different evolution paths follow: either the stellar envelope is quickly lost and no more thermal pulses develop or the AGB phase resumes with additional thermal pulses. | result 0.97 | 0.88 | 0.14 | asserted 0.98 |
| s10 | This behaviour critically depends on the pulse number when the PIE occurs, the mass of the ingested protons, and the extent to which the pulse material is diluted in the convective envelope. | interpretation 0.57 | 0.84 | 0.09 | asserted 1.00 |
| s11 | The surface enrichment after a PIE is a robust feature of our models and it persists under various convective assumptions. | result 0.98 | 0.93 | 0.19 | asserted 1.00 |
| s12 | Our models can synthesise heavy elements up to Pb without any parametrized extra mixing process such as overshoot or inclusion of a $^{13}$C-pocket. | result 0.99 | 0.95 | 0.53 | asserted 0.85 |
| s13 | Nevertheless, it remains to be explored how the i-process depends on mixing processes, such as overshoot, thermohaline, or rotation. | future work 0.91 | 0.08 | 0.04 | hedged possibility 0.53 |
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The paper
Original abstract
Alongside the slow (s) and rapid (r) neutron capture processes, an intermediate neutron capture process (i-process) is thought to exist. It happens when protons are mixed in a convective helium-burning zone, and is referred to as proton ingestion event (PIE). A possible astrophysical site is the asymptotic giant branch (AGB) phase of low-mass low-metallicity stars. We provide i-process yields of a grid of AGB stars experiencing PIEs. We computed 12 models with initial masses of 1, 2, and 3 $M_{\odot}$ and metallicities of [Fe/H] $=-3.0$, $-2.5$ $-2.3,$ and $-2.0, $ with the stellar evolution code STAREVOL. We used a nuclear network of 1160 species at maximum, coupled to the chemical transport equations. These simulations do not include any extra mixing process. Proton ingestion takes place in six out of our 12 AGB models. These models experience i-process nucleosynthesis characterized by neutron densities of $\simeq 10^{14} -10^{15}$ cm$^{-3}$. Depending on the PIE properties two different evolution paths follow: either the stellar envelope is quickly lost and no more thermal pulses develop or the AGB phase resumes with additional thermal pulses. This behaviour critically depends on the pulse number when the PIE occurs, the mass of the ingested protons, and the extent to which the pulse material is diluted in the convective envelope. The surface enrichment after a PIE is a robust feature of our models and it persists under various convective assumptions. Our models can synthesise heavy elements up to Pb without any parametrized extra mixing process such as overshoot or inclusion of a $^{13}$C-pocket. Nevertheless, it remains to be explored how the i-process depends on mixing processes, such as overshoot, thermohaline, or rotation.
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References
How the literature uses it
7 arXiv papers cite this in 15 sentences
Papers citing it · 10 sentences without a confident label
Uses its method or tool 1 paper
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Nuclear reaction rates were taken from the Nuclear Astrophysics Library of the Université Libre de Bruxelles BRUSLIB[http://www.astro.ulb.ac.be/bruslib/] [ref] and the NETGEN interface [ref] (we refer to [ref] and references therein for additional details).
Synthesis of actinides and short-lived radionuclides during i-process nucleosynthesis in AGB stars · AGB models · 0.87
Uses its data or values 1 paper
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In Fig. [ref], we present the n-capture abundance patterns for chemical evolution models without increased MNS r-process production and the yields for low-mass stars as in [ref] for different IMFs.
The chemical DNA of the Magellanic Clouds VI. Origin and evolution of neutron-capture elements in the SMC · i-process from low-mass stars · 0.94
Cites it as background 2 papers
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This was extensively discussed in [ref] .
Synthesis of thorium and uranium in asymptotic giant branch stars · Synthesis of actinides · 0.91
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The supposed i-process sites are metal-poor (MP) AGB stars [ref] and accreting white dwarfs [ref] .
Ba Isotope Ratio in CEMP-s and CEMP-rs Stars as a Signature of s-Process and i-Process · Introduction · 0.88
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