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Na and Mg s-process in low metallicity AGB stars

Na and Mg s-process in low metallicity AGB stars. Sara Bisterzo Roberto Gallino. AGB s-process nucleosynthesis. M = 1.3, 1.5, 2, 3, 5 M sun Different 13 C pocket efficiencies At various [Fe/H]. ENVELOPE COMPOSITION AT THE END OF THE AGB. 5 TPs with TDU. [Fe/H] = - 2.60.

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Na and Mg s-process in low metallicity AGB stars

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  1. Na and Mg s-process in low metallicity AGB stars Sara Bisterzo Roberto Gallino

  2. AGB s-process nucleosynthesis • M = 1.3, 1.5, 2, 3, 5 Msun • Different 13C pocket efficiencies • At various [Fe/H]

  3. ENVELOPE COMPOSITION AT THE END OF THE AGB 5 TPs with TDU [Fe/H] = - 2.60

  4. ENVELOPE COMPOSITION AT THE END OF THE AGB 20 TPs with TDU [Fe/H] = - 2.60

  5. ENVELOPE COMPOSITION AT THE END OF THE AGB 26 TPs with TDU [Fe/H] = - 2.60

  6. ENVELOPE COMPOSITION AT THE END OF THE AGB 35 TPs with TDU [Fe/H] = - 2.60

  7. ENVELOPE COMPOSITION AT THE END OF THE AGB 48 TPs with TDU [Fe/H] = - 2.60

  8. Range of Masses M = 1.3 – 5 Msun For the same 13C pocket (ST case) [Fe/H] = - 2.60

  9. Primary 22Ne in low metallicity stars • The third dredge-up episode mixes with the envelope primary 12C produced by partial He burning in the thermal pulse • The growing H burning shell converts CNO nuclei into 14N, part of which derives from primary 12C • This 14N is further converted to 22Ne at the beginning of the next thermal pulse • In the thermal pulse 22Ne is marginally affected by a captures

  10. A strong primary production of 22Ne results, which increases with pulse number

  11. Primary Na • During the thermal pulse, 23Na is produced by 22Ne(n,g)23Na • Slight depletion of 23Na derives from its low n capture cross section (2mb at 30 keV)  The strong primary production of 22Ne implies a strong primary production of Na

  12. Primary Mg • Solar Mg is made of about 80% 24Mg, 10% 25Mg, 10% 26Mg. • In the TP, the 22Ne(a,g)26Mg and 22Ne(a,n)25Mg reactions feed a strong primary production of 25Mg and 26Mg • Also some primary production of 24Mg derives from 23Na(n,g) 24Na(b-) 24Mg

  13. Na and Mg at different metallicities

  14. CONCLUSIONS: • AGB models of low metallicities predict an important production of primary Na and Mg which may constraint the initial mass of spectroscopic s-enhanced stars

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