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S-Process in C-Rich EMPS: predictions versus observations

S-Process in C-Rich EMPS: predictions versus observations. Sara Bisterzo (1) Roberto Gallino (1) Oscar Straniero (2) I. I. Ivans (3, 4) and Wako Aoki, Sean Ryan, Timoty C. Beers (1) Dipartimento di Fisica Generale , Università di Torino, 10125 (To) Italy

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S-Process in C-Rich EMPS: predictions versus observations

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  1. S-Process in C-Rich EMPS: predictions versus observations Sara Bisterzo (1) Roberto Gallino (1) Oscar Straniero (2) I. I. Ivans (3, 4) and Wako Aoki, Sean Ryan, Timoty C. Beers (1) Dipartimento di Fisica Generale , Università di Torino, 10125 (To) Italy (2) Osservatorio Astronomico di Collurania – Teramo, 64100 (3)The Observatories of the Carnegie Institution of Washington, Pasadena, CA, (USA) (4)Princeton University Observatory, Princeton, NJ (USA)

  2. The AGB engine Convective envelope Neutron source:12C(p,g)13N(b+)13C(a,n). Type: primary When:interpulse T6>90. Where: He-intershell Density:106-107 (n/cm3) 13C(a,n)16O He-intershell TP During the TDU (third dredge-up)  p ingestion in the top of He-intershell (few protons). At H-shell ignition  13C-pocket formation via 12C + p  13N +  , and 13N()13C At T~ 108 K  13C(a,n)16O in radiative conditions  s-process. 22Ne(a,n)25Mg Straniero et al. 1995, Gallino et al. 1998

  3. The two neutron sources in AGB stars 13C(a,n)16O22Ne(a,n)25Mg Needs 13C Major neutron source 13C-pocket Primary source! T8 = 0.9-1 Interpulse phase (1- 0.4) 105 yr Radiative conditions Nn = 107 cm-3 Abundant 22Ne Minor neutron source Neutron burst Secondary (primary) source T8 = 3 (low 22Ne efficiency) Thermal pulse 6 yr Convective conditions Nn (peak)= 1010 cm-3

  4. 1.2 Msun  3 pulses 1.3 Msun  6 pulses 1.4 Msun  8 pulses 1.5 Msun  20 pulses 2 Msun  26 pulses 3 Msun  30 pulses AGB models at very low [Fe/H] 1.2 Msun < M < 3 Msun M = 1.5 Msun 13C-pocket: ST*2 …. ST/100 Constant pulse by pulse (ST: 4.10-6 Msun , [Fe//] = -0.3,Reproduction of Solar Main Component ) Mass loss : from 10-7 to 10-4 Msun/yr  Reimers 1.2 Msun  η = 0.3 1.3 Msun  η = 0.3 1.4 Msun  η = 0.3 1.5 Msun  η = 0.3 2 Msun  η = 0.5 3 Msun  η = 1

  5. At very low metallicity Today, Intrinsic AGB halo stars: typical mass is ~ 0.6 Msun (initial mass 0.8 – 0.9 Msun) • NO TDU  No C or s-process enrichment observable.

  6. Then all CRUMPS are Extrinsic AGB stars: Binary systems transfer of material C- and s-rich on the companion (through stellar wind, Roche Lobe …). The unevolved companion shows the tipical AGB composition, while the true AGB star is now a White Dwarf.

  7. Extrinsic AGB models Diluition factor: used to simulate the mixing effect in the envelope of the extrinsic stars Note: for main sequence stars dil ≈ 0  for giants dil may be important

  8. AGB models: envelope abundances M ≈ 1.5 Msun Pb hs ls

  9. To reproduce stars with both s+r enhancements Different choice of initial chemical abundances of Eu in the progenitor clouds [Eu/Fe]ini from 0.5 to 1.5 and 2.0

  10. Effect of pre r-enrichment in s-enhanced stars AGB star model of M ≈ 1.3 Msun with [Fe/H] = - 2.60. NO r-process rich r-process rich [Eu/Fe]ini = 0.0 [Eu/Fe]ini = 2.0 Model with pre r-enrichment normalized to [Eu/Fe]ini = 2.0 in the parental cloud: the envelope abundances in these stars are predicted by mass transfer from the more massive AGB companion in a binary system which formed from a parental cloud already enriched in r elements.

  11. Choice of initial abundances The choice of the initial r-rich isotope abundances normalised to Eu is made considering the r-process solar prediction from Arlandini et al.1999.

  12. 1- Lead stars (C, s, Pb rich)2 – C and s+r rich Lead stars

  13. 1.8* References 1. J. A. Johnson, M. Bolte, ApJ 579, L87 (2002) 2. W. Aoki, et al., ApJ 580, 1149 (2002) 3. T. Sivarani, et al., A&A 413, 1073 (2004) 4. J. A. Johnson, M. Bolte, ApJ 605, 462 (2004) 5. W. Aoki, et al., ApJ 561, 346 (2001) 6. S. Van Eck, S. Goriely, A. Jorissen, B. Plez, A&A 404, 291 (2003) 7. S. Lucatello, et al., AJ 125, 875 (2003) • 8. J. G. Cohen, N. Christlieb, Y. Z. Quian, G. J. Wasserburg, ApJ 588, 1082 (2003) • 9. B. Barbuy, et al., A&A 429, 1031 (2005) • 11. I. Ivans et al.,ApJ accepted (2005) • [Eu/Fe] measured; **sigma(dil) = ± 0.2 dex • NOTE: Initial Mass are estimates dependent also • on mass loss rates adopted

  14. Teff = 5850 K

  15. Teff = 6625 K

  16. 2 – C and s+r rich Lead stars

  17. HE2148-1247 Cohen et al. 2003 0.0 With r-process enhancement  [Eu/Fe] ini = 2.0 Without r-process enhancement  [Eu/Fe] ini = 0.0 Teff = 6380 K

  18. CS29497-030 Ivans et al. 2005 Prediction updated Extrinsic AGBs indicator Teff = 7000 K Without r-process enhancement  [Eu/Fe] ini = 0.0 With r-process enhancement  [Eu/Fe] ini = 2.0

  19. Zr over Nb: Intrinsic or Extrinsic AGBs Case ST*2 [Eu/Fe]ini = 2.0 M ≈ 1.3 Msun [Fe/H] = -2.60 Fig. 2 s-process path The s elements enhancement in low-metallicity stars interpreted by mass transfer in binary systems (extrinsic AGBs). For extrinsic AGBs [Zr/Nb] ~ 0. Instead, for intrinsic AGBs [Zr/Nb] ~ – 1.

  20. CS29497-34 Barbuy et al. 2005 With r-process enhancement  [Eu/Fe] ini = 1.5 Without r-process enhancement  [Eu/Fe] ini = 0.0 Teff = 4800 K

  21. CS31062-050 Aoki et al. 2002 With r-process enhancement  [Eu/Fe] ini = 1.8 Without r-process enhancement  [Eu/Fe] ini = 0.0 Teff = 5600 K

  22. With r-process enhancement  [Eu/Fe] ini = 1.8 Teff = 5500 K

  23. Barklem et al. 2005: s-enhanced stars

  24. 0

  25. CONCLUSIONS: The spectroscopic abundances of low-metallicity s- and r-process enriched stars are interpreted using theoretical AGB models (FRANEC CODE),with an initial composition already enriched in r elements from the parental cloud from which the binary system was formed. • [Zr/Nb] is an indicator of an extrinsic AGB in a binary system: [Zr/Nb] ~ 0 for an extrinsic AGB, [Zr/Nb] ~ – 1 for an intrinsic AGB. • Spectroscopic determination of [Na/Fe] and [Mg/Fe] permits an estimate of the initial AGB stellar mass.

  26. CONCLUSIONS: • Open Problem: the strong discrepancy of C and N predictions with respect to observations may be reconciled: • by introducing the effect of cool bottom process (CBP) in the TP-AGB phase (*); • for N and [Fe/H] < -2.3, by the effect of Huge First TDU (see Gallino presentation). • Uncertainties in the spectroscopic abundances of C, N, O, Na, Mg  M. Asplund, ARAA 2005 (*) Nollett, K. M., Busso, M., Wasserburg, G. J., ApJ 582, 1036 (2003); Wasserburg, G. J., Busso, M., Gallino, R., Nollett, K. M., (2006), Nucl. Physics, in press.

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