Ba isotopic compositions in stardust SiC grains from the Murchison meteorite: Insights into the stellar origins of large SiC grains

Autor(es)

Avila, Janaina N. ^{[1, 2, 3]} ; Ireland, Trevor R. ^{[2, 3]} ; Gyngard, Frank ^{[4, 5]} ; Zinner, Ernst ^{[4, 5]} ; Mallmann, Guilherme ^{[6, 2]} ; Lugaro, Maria ^[7] ; Holden, Peter ^[2] ; Amari, Sachiko ^{[4, 5]}

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Dept Astron, IAG, BR-05508090 Sao Paulo - Brazil

^[2] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200 - Australia

^[3] Australian Natl Univ, Planetary Sci Inst, Canberra, ACT 0200 - Australia

^[4] Washington Univ, Dept Phys, St Louis, MO 63130 - USA

^[5] Washington Univ, Space Sci Lab, St Louis, MO 63130 - USA

^[6] Univ Sao Paulo, Inst Geosci, BR-05508080 Sao Paulo - Brazil

^[7] Monash Univ, Monash Ctr Astrophys, Clayton, Vic 3800 - Australia

• Tipo de documento: Artigo Científico
• Fonte: GEOCHIMICA ET COSMOCHIMICA ACTA; v. 120, p. 628-647, NOV 1 2013.
• Citações Web of Science: 12

Resumo

We report barium isotopic measurements in 12 large (7-58 mu m) stardust silicon carbide grains recovered from the Murchison carbonaceous chondrite. The C-, N-, and Si-isotopic compositions indicate that all 12 grains belong to the mainstream population and, as such, are interpreted to have condensed in the outflows of low-mass carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. Barium isotopic analyses were carried out on the Sensitive High Resolution Ion Microprobe -Reverse Geometry (SHRIMP-RG) with combined high mass resolution and energy filtering to eliminate isobaric interferences from molecular ions. Contrary to previous measurements in small (< 5 lm) mainstream grains, the analyzed large SiC grains do not show the classical s-process enrichment, having near solar Ba isotopic compositions. While contamination with solar material is a common explanation for the lack of large isotopic anomalies in stardust SiC grains, particularly for these large grains which have low trace element abundances, our results are consistent with previous observations that Ba isotopic ratios are dependent on grain size. We have compared the SiC data with theoretical predictions of the evolution of Ba isotopic ratios in the envelopes of low-mass AGB stars with a range of stellar masses and metallicities. The Ba isotopic measurements obtained for large SiC grains from the LS + LU fractions are consistent with grain condensation in the envelope of very low-mass AGB stars (1.25 M-circle dot) with close-to-solar metallicity, which suggests that conditions for growth of large SiC might be more favorable in very low-mass AGB stars during the early C-rich stages of AGB evolution or in stable structures around AGB stars whose evolution was cut short due to binary interaction, before the AGB envelope had already been largely enriched with the products of s-process nucleosynthesis. (C) 2013 Elsevier Ltd. All rights reserved. (AU)

• Processo FAPESP: 10/05512-1 - Estudos experimentais de acresção e diferenciação planetária
• Beneficiário: Guilherme Mallmann
• Modalidade de apoio: Auxílio à Pesquisa - Jovens Pesquisadores