Production of Lithium and Heavy Elements in AGB Stars Experiencing PIEs
Asymptotic giant branch (AGB) stars can experience proton ingestion events (PIEs), leading to a rich nucleosynthesis. During a PIE, the intermediate neutron capture process (i-process) develops, leading to the production of trans-iron elements. It is also suggested that lithium is produced during th...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-10-01
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| Series: | Galaxies |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2075-4434/12/5/66 |
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| Summary: | Asymptotic giant branch (AGB) stars can experience proton ingestion events (PIEs), leading to a rich nucleosynthesis. During a PIE, the intermediate neutron capture process (i-process) develops, leading to the production of trans-iron elements. It is also suggested that lithium is produced during these events. We investigate the production of lithium and trans-iron elements in AGB stars experiencing a PIE with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1</mn><mo><</mo><msub><mi>M</mi><mi>ini</mi></msub><mo>/</mo><msub><mi>M</mi><mo>⊙</mo></msub><mo><</mo><mn>3</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mn>3</mn><mo><</mo><mo>[</mo><mi>Fe</mi><mo>/</mo><mi mathvariant="normal">H</mi><mo>]</mo><mo><</mo><mn>0</mn></mrow></semantics></math></inline-formula>. We find that lithium is produced in all PIE models with surface abundances <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>3</mn><mo><</mo></mrow></semantics></math></inline-formula> A(Li) <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo><</mo><mn>5</mn></mrow></semantics></math></inline-formula>. The surface enrichment and overall AGB lithium yield increases with decreasing stellar mass. The lithium enrichment is accompanied by a production of <sup>13</sup>C with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>3</mn><msup><mo><</mo><mn>12</mn></msup></mrow></semantics></math></inline-formula>C/<sup>13</sup>C <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo><</mo><mn>9</mn></mrow></semantics></math></inline-formula> at the surface just after the PIE. AGB stars experiencing PIE may be related to J-type carbon stars whose main features are excesses of lithium and<sup>13</sup>C. In addition to Li and <sup>13</sup>C, heavy elements (e.g., Sr, Ba, Eu, Pb) are significantly produced in low-metallicity stars up to [Fe/H] <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>≃</mo><mo>−</mo><mn>1</mn></mrow></semantics></math></inline-formula>. The yields of our models are publicly available. Additionally, of interest to the Li nucleosynthesis, we provide an updated fitting formula for the <sup>7</sup>Be(<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>e</mi><mo>−</mo></msup><mo>,</mo><msub><mi>ν</mi><mi>e</mi></msub></mrow></semantics></math></inline-formula>)<sup>7</sup>Li electron capture rate. |
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| ISSN: | 2075-4434 |