Presolar Silicon Carbide Grains of Types Y and Z: Their Strontium and Barium Isotopic Compositions and Stellar Origins

Abstract

We report the Sr and Ba isotopic compositions of 18 presolar SiC grains of types Y (11) and Z (7), rare types commonly argued to have formed in lower-than-solar metallicity asymptotic giant branch (AGB) stars. We find that the Y and Z grains show higher 88Sr/87Sr and more variable 138Ba/136Ba ratios than mainstream (MS) grains. According to FRANEC Torino AGB models, the Si, Sr, and Ba isotopic compositions of our Y and Z grains can be consistently explained if the grains came from low mass AGB stars with 0.15 Zsun <= Z < 1.00 Zsun, in which the 13C neutron exposure for the slow neutron-capture process is greatly reduced with respect to that required by MS grains for a 1.0 Z8 AGB star. This scenario is in line with the previous finding based on Ti isotopes, but it fails to explain the indistinguishable Mo isotopic compositions of MS, Y, and Z grains.

Accepted by EPJA

References in corpus (15)

• Barium Isotopic Composition of Mainstream Silicon Carbides from Murchison: Constraints for s-Process Nucleosynthesis in AGB Stars
• Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
• Stellar origin of 15N-rich presolar SiC grains of type AB: supernovae with explosive hydrogen burning
• Magnetic-buoyancy Induced Mixing in AGB Stars: Presolar SiC Grains
• MHD and deep mixing in evolved stars. 1. 2D and 3D analytical models for the AGB
• Re-evaluation of the ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg and ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reaction rates
• Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities
• J-type carbon stars: A dominant source of 14N-rich presolar SiC grains of type AB
• Late formation of silicon carbide in type II supernovae
• Origin of large meteoritic SiC stardust grains in metal-rich AGB stars
• Cluster analysis of presolar silicon carbide grains: evaluation of their classification and astrophysical implications
• The stellar beta-decay rate of 134Cs and its impact on the Barium nucleosynthesis in the s process
• Theoretical estimate of the half-life for the radioactive ${}^{134}$Cs and ${}^{135}$Cs in astrophysical scenarios
• New Multielement Isotopic Compositions of Presolar SiC Grains: Implications for Their Stellar Origins
• Slow Neutron-Capture Process: Low-mass AGB stars and presolar silicon carbide grains

Cited by in corpus (2)

• Presolar grains
• 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