Heavy Element Abundances in Presolar Silicon Carbide Grains from Low-Metallicity AGB Stars

TL;DR

This study analyzes presolar silicon carbide grains from low-metallicity AGB stars, revealing higher trace element concentrations and correlations consistent with stellar models, confirming their stellar origins.

Contribution

It provides detailed isotopic and trace element data for presolar SiC grains, linking them to low-metallicity AGB star sources and enhancing understanding of stellar nucleosynthesis.

Findings

Y and Z grains have higher Zr and Ba concentrations than mainstream grains.

Positive correlation between Ba concentrations and s-process Si in Y and Z grains.

Results match predictions for 2-3 Msun AGB stars with subsolar metallicity.

Abstract

Primitive meteorites contain small amounts of presolar minerals that formed in the winds of evolved stars or in the ejecta of stellar explosions. Silicon carbide is the best studied presolar mineral. Based on its isotopic compositions it was divided into distinct populations that have different origins: Most abundant are the mainstream grains which are believed to come from 1.5-3 Msun AGB stars of roughly solar metallicitiy. The rare Y and Z grains are likely to come from 1.5-3 Msun AGB stars as well, but with subsolar metallicities (0.3-0.5x solar). Here we report on C and Si isotope and trace element (Zr, Ba) studies of individual, submicrometer-sized SiC grains. The most striking results are: (1) Zr and Ba concentrations are higher in Y and Z grains than in mainstream grains, with enrichments relative to Si and solar of up to 70x (Zr) and 170x (Ba), respectively. (2) For the Y and Z grains there is a positive correlation between Ba concentrations and amount of s-process Si. This correlation is well explained by predictions for 2-3 Msun AGB stars with metallicities of 0.3-0.5x solar. This confirms low-metallicity stars as most likely stellar sources for the Y and Z grains.