Regular Article - Experimental Physics
Presolar silicon carbide grains of types Y and Z: their strontium and barium isotopic compositions and stellar origins
Laboratory for Space Sciences and Physics Department, Washington University in St. Louis, 63130, St. Louis, MO, USA
2 McDonnell Center for the Space Sciences, Washington University in St. Louis, 63130, St. Louis, MO, USA
3 Earth and Planets Laboratory, Carnegie Institution for Science, 20015, Washington, DC, USA
4 Department of the Geophysical Sciences, The University of Chicago, 60637, Chicago, IL, USA
5 Chicago Center for Cosmochemistry, Chicago, IL, USA
6 INAF-Osservatorio Astronomico d’Abruzzo, 64100, Teramo, Italy
7 INFN-Sezione di Perugia, 06123, Perugia, Italy
8 Institute for Applied Physics, Goethe University Frankfurt, 60438, Frankfurt, Germany
9 Dipartimento di Fisica, Università di Torino, 10125, Turin, Italy
10 The Enrico Fermi Institute, The University of Chicago, 60637, Chicago, IL, USA
Accepted: 21 September 2022
Published online: 10 November 2022
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.
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