AGB models at very low metallicities

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AGB models at very low metallicities
S. Cristallo (INAF - Osservatorio Astronomico di
Teramo)
Collaborators O. Straniero, R. Gallino, L.
Piersanti, I.
Domínguez, F. Käppeler
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What happens at very low metallicities
Hollowell et al. (1990) Fujimoto et al.
(2000) Iwamoto et al. (2004) Suda et al.
(2004) Straniero et al. (2004) Campbell et al.
(2007)
Cristallo et al. (2007), ApJ 667 489
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Low metallicity low mass AGBs
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The proton ingestion mechanism
M 1.5 M? Z 5.0x10-5

• Low time steps ?Time dependent mixing
• Rapid structure reaction ?Coupling between
  phisical and chemical evolution
• Large neutron densities (nn1015 cm-3) ? LARGE
  NUCLEAR NETWORK

500 isotopes ? 700 isotopes 700 reactions ? 1200
reactions
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ENERGETICS
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TEMPERATURE
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C H E M I S T R Y
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The Models
Z5x10-5
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Effects of the Huge Pulse (I)
12C/13C
Nitrogen
Even very low mass AGB show C- and s-process
enhancement
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Effects of the Huge Pulse (II)
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Huge Pulse, Molecular Opacities and Mass-loss

• The temperature structure of the envelope
  changes
• the stars become cooler
• ? the mass-loss increases

Cristallo et al. 2007 (ApJ 667, 489)
? and with the Huge Pulse?
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M 2.5 M?
M 2 M?
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The importance of using a FULL nuclear network
FULL
REDUCED
(corresponding to ROBERTOs cases ST/6 ST/8)
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WARNINGS

• The amount of oxygen enhancement
• Mass-loss law at low metallicities
• Dependence of results on the adopted mixing
  scheme
• Neutron cross sections of unstable isotopes far
  from the ß stability valley.

IN THE FUTURE

• Explore a wider range of metallicities.