The production of germanium in asymptotic giant branch stars

Amanda Karakas, Maria Lugaro, Roberto Gallino

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearchpeer-review

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 languageEnglish
Title of host publicationProceedings of Science
Subtitle of host publicationInternational Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX
PublisherSissa Medialab, SRL
Number of pages6
DOIs
Publication statusPublished - 1 Dec 2006
Externally publishedYes
EventInternational Symposium on Nuclear Astrophysics 2006: Nuclei in the Cosmos - IX - Geneva, Switzerland
Duration: 25 Jun 200630 Jun 2006
Conference number: 9th
https://pos.sissa.it/028/

Publication series

NameProceedings of Science
PublisherSissa Medialab, SRL
Volume028
ISSN (Print)1824-8039

Conference

ConferenceInternational Symposium on Nuclear Astrophysics 2006
Abbreviated titleNIC 2006
Country/TerritorySwitzerland
CityGeneva
Period25/06/0630/06/06
Internet address

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