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Presolar silicon carbide grains of types Y and Z: their strontium and barium isotopic compositions and stellar origins

Journal
Date Issued
2022
Author(s)
Liu, Nan
•
Stephan, Thomas
•
•
•
Gallino, Roberto
•
Nittler, Larry R.
•
Alexander, Conel M.O’ D.
•
Davis, Andrew M.
DOI
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 Z⊙ ≤ Z < 1.00 Z⊙, 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 Z⊙ 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.
Volume
58
Issue
11
Uri
Url
Issn Identifier
1434-6001
Rights
open.access
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