Simon Campbell1,2

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A Grid of Low- and Intermediate-mass EMP
ModelsStructure, Nucleosynthetic Yields the
CEMPs

• Simon Campbell1,2 John Lattanzio2
• 1) ASIAA, Taiwan (Academia Sinica Institute of
  Astronomy and Astrophysics)
• 2) CSPA, Australia (Centre for Stellar and
  Planetary Astrophysics at Monash University)

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Talk Contents

• PART 1 Our Grid of EMP Models
• Overview of peculiar evolution
• Overview of pollution results
• PART 2 Confronting the Chemical Yields
  with CEMP Observations
• Single elements C N
• Abundance patterns

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PART 1A Grid of Low and Intermediate Mass EMP
Z0 Stellar Models
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The Low-Metallicity Universe in Perspective
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This Study Exploring EMP Stellar Evolution
Nucleosynthesis at LM and IM

• We have calculated a grid of stellar models
  including
• Structural evolution from MS to end of TP-AGB
• Nucleosynthetic evolution for nuclides up to
  Sulphur 35
• Yields for the 74 included species

Stellar structure code MONSTAR (Monash/Mt
Stromlo code)
- Standard 1D stellar code Diffusive Mixing
- No
overshoot used (gt Schwarzschild
boundary) Nucleosynthesis code MONSN (monsoon,
Monash code)
- Post-process code, 500 reactions
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Some Results
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The Dual Core Flash (DCF)

• The normal core He flash convective zone (in
  low-mass stars) breaks through H-He
  discontinuity.
• gt Protons mixed down H Flash
• He burning products mixed up.
• This material is later mixed up into the
  envelope, polluting the surface.
• Fujimoto et al. (1990) suggested that the excess
  C in the CEMPs may come from these peculiar
  surface pollution events occurring in Zero
  Metallicity (Z0) and EMP stars.

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• An Aside
• Possible s-Process
• in the DCF HeCZ?
• During the DCF proton ingestion episode (PIE)
  the 13C(?,n)16O reaction supplies many neutrons.
• Peak neutron density at bottom of HeCZ
• Needs further investigation.

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The Dual Shell Flash (DSF)

• Similar to the Dual Core Flash but this time it
  is the AGB shell helium flash convective zone
  that breaks through the H-He discontinuity.
• Again protons are mixed down, He burning products
  mixed up.
• This material is also later mixed up into the
  envelope, polluting the surface.

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Example of AGB Nucleosynthesis M 3.0
Msun Fe/H -5.45
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Pollution Summary for the Grid of
Models The mass-Fe/H plane
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Pollution Summary in the HRD
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PART 2Confronting the Yields with CEMP
Abundance Observations
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The Problem Carbon-rich EMP Halo Stars (CEMPs)
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Carbon Yields Across the Grid of Models
(NB Other element plots in my thesis at
www.asiaa.sinica.edu.tw/simcam)
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Integrated Model Yields Vs Observations
C/Fe
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Integrated Model Yields Vs Observations C/N
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PART 2bConfronting the Yields with CEMP
Abundance Patterns
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3 Abundance patterns from 4 stars!
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Yields Vs Observed Abund Patterns Fe/H-5.5
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Yield Tables are available for -6.5 lt Fe/H lt
-3.0 and Z0M 0.85, 1.0, 2.0, 3.0 MsunCaveat
Many uncertainties!
The End! )
simcam_at_asiaa.sinica.edu.tw