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  Correlated nanoscale characterization of a unique complex oxygen-rich stardust grain: Implications for circumstellar dust formation

Leitner, J., Hoppe, P., Floss, C., Hillion, F., & Henkel, T. (2018). Correlated nanoscale characterization of a unique complex oxygen-rich stardust grain: Implications for circumstellar dust formation. Geochimica et Cosmochimica Acta, 221, 255-274. doi:10.1016/j.gca.2017.05.003.

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Leitner, J.1, Author              
Hoppe, P.1, Author              
Floss, C., Author
Hillion, F., Author
Henkel, T., Author
Affiliations:
1Particle Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826291              

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 Abstract: We report the light to intermediate-mass element abundances as well as the oxygen, magnesium, silicon, and titanium isotope compositions of a unique and unusually large (0.8 µm × 3.75 µm) presolar O-rich grain from the Krymka LL3.2 chondrite. The O-, Al-, and Ti-isotopic compositions are largely compatible with an origin from an asymptotic giant branch (AGB) star of 1.5 solar masses with a metallicity that is 15% higher than the solar metallicity. The grain has an elevated 17O/16O ratio (8.40 ± 0.16 × 10−4) compared to solar, and slightly sub-solar 18O/16O ratio (1.83 ± 0.03 × 10−3). It shows evidence for the presence of initial 26Al, suggesting formation after the first dredge-up, during one of the early third dredge-up (TDU) episodes. Titanium isotopic data indicate condensation of the grain before significant amounts of material from the He-burning shell were admixed to the stellar surface with progressive TDUs. We observed a small excess in 30Si (δ30Si = 41 ± 5‰), which most likely is inherited from the parent star’s initial Si-isotopic composition. For such stars stellar models predict a C/O-ratio < 1 even after the onset of TDU, thus allowing the condensation of O-rich dust. The grain is an unusual complex presolar grain, consisting of an Al-Ca-Ti-oxide core, surrounded by an Mg-Ca-silicate mantle, and resembles the condensation sequence for a cooling gas of solar composition at pressures and dust/gas ratios typically observed for circumstellar envelopes around evolved stars. We also report the first observation of phosphorus in a presolar grain, although the origin of the P-bearing phase remains ambiguous.

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Language(s): eng - English
 Dates: 20172018
 Publication Status: Published online
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 Rev. Type: Peer
 Identifiers: DOI: 10.1016/j.gca.2017.05.003
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Title: Geochimica et Cosmochimica Acta
  Abbreviation : Geochim. Cosmochim. Acta
Source Genre: Journal
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Publ. Info: Oxford : Pergamon
Pages: - Volume / Issue: 221 Sequence Number: - Start / End Page: 255 - 274 Identifier: ISSN: 0016-7037
CoNE: https://pure.mpg.de/cone/journals/resource/954925401558