On the Mass and Metallicity Distributions of the Parent AGB Stars of O-rich Presolar Stardust Grains

TL;DR

This study uses Monte Carlo simulations to analyze the mass and metallicity of AGB stars that produced O-rich presolar grains, revealing insights into stellar evolution and the Galaxy's chemical history.

Contribution

It introduces a simple Monte Carlo model to interpret presolar grain data, constraining the masses and metallicities of their parent AGB stars and exploring Galactic chemical evolution.

Findings

Presolar grains originate from AGB stars of 1.15-2.2 solar masses.

The Galaxy had a moderate age-metallicity relationship with significant scatter.

The Sun's isotopic ratios suggest it had a lower metallicity or unusual isotopic composition.

Abstract

Presolar grains in meteorites formed in a sample of AGB stars that ended their lives within ~1 Gyr of the origin of the Solar System 4.6 Gyr ago. The O-isotopic compositions of presolar O-rich stardust reflect the masses and metallicities of their parent stars. We present simple Monte Carlo simulations of the parent AGB stars of presolar grains. Comparison of model predictions with the grain data allow some broad conclusions to be drawn: 1) Presolar O-rich grains formed in AGB stars of mass ~1.15 - 2.2 MSun. The upper-mass cutoff reflects dredge-up of C in more massive AGB stars, leading to C-rich dust rather than O-rich, but the lack of grains from intermediate-mass AGB stars (>4MSun) is a major puzzle. 2) The grain O-isotopic data are reproduced well if the Galaxy in presolar times was assumed to have a moderate age-metallicity relationship, but with significant metallicity scatter for stars born at the same time. 3) The Sun appears to have a moderately low metallicity for its age and/or unusual 17O/16O and 18O/16O ratios for its metallicity. 4) The Solar 17O/18O ratio, while unusual relative to present-day molecular clouds and protostars, was not atypical for the presolar disk and does not require self-pollution of the protosolar molecular cloud by supernova ejecta.