On the mass and metallicity distributions of the parent AGB stars of presolar grains

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On the mass and metallicity distributions of the
parent AGB stars of presolar grains
Larry R. Nittler Department of Terrestrial
Magnetism Carnegie Institution of Washington
Gallino-Fest Sep 2008, Torino
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Isotope anomalies workshop, Washington
University, Nov 1993
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Presolar Grains and Galactic Evolution

• Presolar stardust compositions reflect interplay
  of galactic chemical evolution, nucleosynthesis,
  physicochemical conditions of stellar dust
  formation
• Represent sample of stars that was present
  shortly before formation of Solar System but had
  formed over long history of galactic disk.
• Complementary dataset to astronomical
  observations on Galactic Chemical Evolution

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• Most presolar grains from AGB stars
• Can we infer mass/metallicity distributions for
  parent stars?
• Consistent with expectations from
  models/observations?
• Is there an age-metallicity relationship in Milky
  Way?
• Is the Suns O-isotopic composition anomalous?
• Is there evidence for local evolution (e.g.
  galactic mergers)?

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Presolar AGB dust

• Oxides/Silicates
• 200 ppm in primitive meteorites
• O isotopes indicate most formed in low-mass AGB
  stars
• SiC
• 50ppm
• C, Al, Ne, Mo, Ba, Zr, Ne isotopes indicate AGB
  origin for gt90
• Graphite
• 10ppm
• C, heavy-element isotopes, s-process enriched
  sub-grains indicate (low-metallicity) AGB origin
  for majority.

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O-isotope MC simulations

• Randomly select parent star masses from IMF
  (Salpeter 1955 NM-2.35)
• Min, Max masses are parameters
• Metallicity Distribution
• AMR Assume Fe/Habt, select value for each
  stellar mass, based on lifetime and assumed
  scatter (params a, b, s)
• No AMR Assume no age-metallicity relationship
  (params are average Fe/H and s)
• Compare O isotopic dredge-up values for resulting
  M,Z distributions with oxide/silicates
• Interpolate DUP models of Boothroyd Sackmann
  (1999)

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• Peak in First Dredge-up curve for 17O/16O versus
  mass
• 17O/16O distribution thus sensitive measure of
  maximum mass

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Data indicate maximum mass for parent stars of
2.2 M? Similar analysis indicates lower limit
of 1.15 M?
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Most O-rich grains from different stars than SiC
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Where are the IMS grains??? Should be 50
(GailHoppe)
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Is there an age-metallicity relationship in the
Milky Way?
YES (Edvardsson et al. 1993, Reddy et al. 2003,
Haywood 2006)
NO (Nordström et al. 2004 Feltzing et al. 2001)
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Age-metallicity relationship?

• Monte Carlo simulations better match to data with
  AMR than without
• Requires 0.04-0.06 dex range of Fe/H (10-15
  of Z) at any given time (model-dependent)

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Age-metallicity relationship?

• Monte Carlo simulations better match to data with
  AMR than without
• Requires 0.04-0.06 dex range of Fe/H (10-15
  of Z) at any given time (model-dependent)

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• Haywood (2006) AMR

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• Haywood (2006) AMR

• MC distribution parallel to Haywood, scatter
  smaller than observational error, offset to
  slightly higher Fe/H (effect of O isotope GCE
  assumptions)

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Is 18O/17O anomalous in the Sun?

• Sun 5.2
• ISM 3 (WilsonRood ARAA 94)
• Nearby protostars 3 (Young et al 2008)
• Is Sun anomalous for age/location?
• Self-Pollution in parent molecular cloud?
  (Prantzos et al. 1996, Young et al 2008)

Prantzos et al AA (1996)
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18O/17O ratio?

• Poor match to data
• Cannot explain grains with 18O/17Ogt3.5
• Suns 18/17 ratio typical of stars forming for
  several Gyr before
• Not effect of molecular cloud self-enrichment
• Galactic merger (D. D. Clayton, 2004)?

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SiC
Nittler and Alexander (2003)
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Presolar Galactic Merger?(D. D. Clayton 2003)

• Explains SiC isotopic correlation lines (Si, Ti)

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Presolar galactic merger?

• Max 12C/13C decreases with increasing 29Si/28Si
• Larger 12C/13C requires higher mass AGB stars (gt3
  M? for Y grains)
• Shorter lived
• Implies temporal evolution to lower 29Si/28Si
  ratios.
• Increasing mixing fraction from merging galaxy?
• Solar/oxide 18O/17O ratio also possibly explained
  (D. D. Clayton 2004)

More than 3700 grains plotted Nittler
Alexander 2003
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Conclusions

• Monte Carlo simulations can reproduce O-isotopes
  of presolar O-rich grains
• Indicate parents stars of mass 1.1-2.3 M?
• Indicate age-metallicity relationship in presolar
  solar neighborhood of MW
• Indicate solar 18O/17O not atypical of stars of
  its metallicity (not due to late input in parent
  molecular cloud)
• Most SiC grains from 1.5 3 M? AGB stars
• Si and C isotopes in SiC grains support presolar
  galactic merger suggestion