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Germanium Production in Asymptotic Giant Branch Stars: Implications for Observations of Planetary Nebulae

Karakas, Amanda; Lugaro, Maria Anna; Gallino, Roberto

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Observations of planetary nebulae (PNe) in the work of Sterling, Dinerstein, & Bowers have revealed abundances in the neutron-capture element germanium (Ge) from solar to factors of 3-10 above solar. The enhanced Ge is an indication that the slow neutron-capture process (the s-process) operated in the parent star during the thermally pulsing asymptotic giant branch (TP-AGB) phase. We compute the detailed nucleosynthesis of a series of AGB models to estimate the surface enrichment of Ge near the...[Show more]

dc.contributor.authorKarakas, Amanda
dc.contributor.authorLugaro, Maria Anna
dc.contributor.authorGallino, Roberto
dc.date.accessioned2015-12-10T22:56:39Z
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/1885/60319
dc.description.abstractObservations of planetary nebulae (PNe) in the work of Sterling, Dinerstein, & Bowers have revealed abundances in the neutron-capture element germanium (Ge) from solar to factors of 3-10 above solar. The enhanced Ge is an indication that the slow neutron-capture process (the s-process) operated in the parent star during the thermally pulsing asymptotic giant branch (TP-AGB) phase. We compute the detailed nucleosynthesis of a series of AGB models to estimate the surface enrichment of Ge near the end of the AGB. A partial mixing zone of constant mass is included at the deepest extent of each dredge-up episode, resulting in the formation of a13C pocket in the top approximately one-tenth of the He-rich intershell. All of the models show surface increases of [Ge/Fe] ≲ 0.5, except the 2.5 M⊙, Z = 0.004 case, which produced a factor of 6 enhancement of Ge. Near the tip of the TP-AGB, a couple of extra thermal pulses (TPs) could occur to account for the composition of the most Ge-enriched PNe. Uncertainties in the theoretical modeling of AGB stellar evolution might account for larger Ge enhancements than we predict here. Alternatively, a possible solution could be provided by the occurrence of a late TP during the post-AGB phase. Difficulties related to spectroscopic abundance estimates also need to be taken into consideration. Further study is required to better assess how the model uncertainties affect the predictions and, consequently, if a late TP should be invoked.
dc.publisherIOP Publishing
dc.sourceAstrophysical Journal, The
dc.subjectKeywords: Nuclear reactions, nucleosynthesis, abundances; Planetary nebulae: general; Stars: AGB and post-AGB
dc.titleGermanium Production in Asymptotic Giant Branch Stars: Implications for Observations of Planetary Nebulae
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume656
dc.date.issued2007
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationu4167262xPUB533
local.type.statusPublished Version
local.contributor.affiliationKarakas, Amanda, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationLugaro, Maria Anna, Utrecht University
local.contributor.affiliationGallino, Roberto, Universita di Torino
local.description.embargo2037-12-31
local.bibliographicCitation.issue2
local.bibliographicCitation.startpageL73
local.bibliographicCitation.lastpageL76
local.identifier.doi10.1086/512676
dc.date.updated2015-12-10T07:55:26Z
local.identifier.scopusID2-s2.0-33847706069
CollectionsANU Research Publications

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