Barium Isotopic Composition of Mainstream Silicon Carbides from Murchison: Constraints for s-Process Nucleosynthesis in AGB Stars

Abstract

We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in $\delta$(${}^{138}$Ba/${}^{136}$Ba) values are found, down to $-$400 permil, which can only be modeled with a flatter ${}^{13}$C profile within the ${}^{13}$C pocket than is normally used. The dependence of $\delta$(${}^{138}$Ba/${}^{136}$Ba) predictions on the distribution of ${}^{13}$C within the pocket in AGB models allows us to probe the ${}^{13}$C profile within the ${}^{13}$C pocket and the pocket mass in asymptotic giant branch (AGB) stars. In addition, we provide constraints on the ${}^{22}$Ne$(\alpha ,n{)}^{25}$Mg rate in the stellar temperature regime relevant to AGB stars, based on $\delta$(${}^{134}$Ba/${}^{136}$Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative $\delta$(${}^{134}$Ba/${}^{136}$Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process ($i$-process), which is activated by the Very Late Thermal Pulse (VLTP) during the post-AGB phase and characterized by a neutron density much higher than the $s$-process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two $p$-process isotopes, ${}^{130}$Ba and ${}^{132}$Ba, in single SiC grains. These isotopes are destroyed in the $s$-process in AGB stars. By comparing their abundances with respect to that of ${}^{135}$Ba, we conclude that there is no measurable decay of ${}^{135}$Cs ($t_{1/2}$= 2.3 Ma) to ${}^{135}$Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before ${}^{135}$Cs decayed.

Cited by in corpus (29)

• i-process nucleosynthesis and mass retention efficiency in He-shell flash evolution of rapidly accreting white dwarfs
• Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
• Magnetic-buoyancy Induced Mixing in AGB Stars: Presolar SiC Grains
• Galactic Chemical Evolution: the Impact of the 13C-pocket Structure on the s-process Distribution
• Constraints of the physics of low-mass AGB stars from CH and CEMP stars
• The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains
• The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
• J-type carbon stars: A dominant source of 14N-rich presolar SiC grains of type AB
• Origin of large meteoritic SiC stardust grains in metal-rich AGB stars
• Coordinated Analysis of Two Graphite Grains from the CO3.0 LAP 031117 Meteorite: First Identification of a CO Nova Graphite and a Presolar Iron Sulfide Subgrain
• s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains
• Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements
• On the mass and metallicity distribution of parent AGB stars of presolar SiC
• The stellar beta-decay rate of 134Cs and its impact on the Barium nucleosynthesis in the s process
• Enrichment of the Galactic disc with neutron capture elements: Sr
• Synthesis of thorium and uranium in asymptotic giant branch stars
• A strong neutron burst in jet-like supernovae of spinstars
• Slow Neutron-Capture Process: Low-mass AGB stars and presolar silicon carbide grains
• Presolar Silicon Carbide Grains of Types Y and Z: Their Strontium and Barium Isotopic Compositions and Stellar Origins
• Presolar grains
• Isotopic ratios for C, N, Si, Al, and Ti in C-rich presolar grains from massive stars
• The ${}^{22}$Ne($\alpha$,n)${}^{25}$Mg reaction -- state of the art, astrophysics, and perspectives
• Representation of s-process abundances for comparison to data from bulk meteorites
• First models of s process in AGB stars of solar metallicity for the stellar evolutionary code ATON with a novel stable explicit numerical solver
• Silicon Isotopic Composition of Mainstream Presolar SiC Grains Revisited: The Impact of Nuclear Reaction Rate Uncertainties
• Impact of $\text{T}$- and $\rho$-dependent decay rates and new (n,$\gamma$) cross sections on the $\text{s}$ process in low-mass AGB stars
• Production of n-rich nuclei in red giant stars
• The ${}^{13}C$-pockets in AGB Stars and Their Fingerprints in Mainstream SiC Grains
• Oxygen and Aluminum-Magnesium Isotopic Systematics of Presolar Nanospinel Grains from CI Chondrite Orgueil