Abstract
Observations of planetary nebulae by Sterling, Dinerstein and Bowers have revealed enhancements in the element Germanium (Ge) by factors of 3 to 10 compared to solar. Germanium can be produced by slow-neutron capture (s-process) in asymptotic giant branch (AGB) stars. We compute the detailed nucleosynthesis of a series of AGB models of variousmasses (1.9 to 6.5M⊙) and metallicities from the zero-aged main sequence to near the end of the thermally-pulsing AGB phase. We include a partial mixing zone of constant mass at the deepest extent of each dredgeup episode. During the interpulse period this mixing zone will produce a 13C pocket in the top ∼1/10th of the He-rich intershell, releasing free neutrons that can be captured by iron-seed nuclei. Using a post-processing code that includes 156 species, 1260 reaction rates and time-dependent convective mixing, we follow the nucleosynthesis of all stable isotopes up to 75As, including the five stable Ge isotopes. The surface Ge abundance at the end of the evolution was not enhanced in models with no partial mixing i.e. [Ge/Fe] ≈ 0, except the 6.5M⊙ models which had [Ge/Fe] ≈ 0.2. Models with partial mixing produced surface enhancements of at most a factor of 3.6, i.e. [Ge/Fe] . 0.5 except the 2.5M⊙, Z = 0.004 model with [Ge/Fe] = 0.77. Given the difficulties in matching the compositions of the most Ge-enriched PNe we suggest a late thermal pulse mixed pure He-intershellmaterial, enriched in Ge, with the small amount of remaining convective envelope.
Original language | English |
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Title of host publication | Proceedings of Science |
Subtitle of host publication | International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX |
Publisher | Sissa Medialab, SRL |
Number of pages | 6 |
DOIs | |
Publication status | Published - 1 Dec 2006 |
Externally published | Yes |
Event | International Symposium on Nuclear Astrophysics 2006: Nuclei in the Cosmos - IX - Geneva, Switzerland Duration: 25 Jun 2006 → 30 Jun 2006 Conference number: 9th https://pos.sissa.it/028/ |
Publication series
Name | Proceedings of Science |
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Publisher | Sissa Medialab, SRL |
Volume | 028 |
ISSN (Print) | 1824-8039 |
Conference
Conference | International Symposium on Nuclear Astrophysics 2006 |
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Abbreviated title | NIC 2006 |
Country/Territory | Switzerland |
City | Geneva |
Period | 25/06/06 → 30/06/06 |
Internet address |