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