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The s-process in massive stars: the shell C-burning contribution

The s-process in massive stars: the shell C-burning contribution. Marco Pignatari Universita’ di Torino. NIC IX conference – 25-30 June, 2006. Kippenhahn’s Diagram for a star with M= 25 M(sun) and solar metallicity (Limongi & Chieffi 2000, ApJ). In the C shell: C-burning:

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The s-process in massive stars: the shell C-burning contribution

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  1. The s-process in massive stars:the shell C-burning contribution Marco Pignatari Universita’ di Torino NIC IX conference – 25-30 June, 2006

  2. Kippenhahn’s Diagram for a star with M= 25 M(sun) and solar metallicity (Limongi & Chieffi 2000, ApJ)

  3. In the C shell: C-burning: 12C(12C,α)20Ne, α-source ((α,n) channels are activated!) 12C(12C,p)23Na, p-source 12C(12C,n)23Mg*, negligible 16O is the most abundant isotope (~ 0.7)

  4. Si 28 29 30 Al 27 Mg 24 25 26 Na 23 Ne 20 21 22 F 19 + α-captures + p-captures 16 17 18 O 14 15 N C 12 13

  5. Photodisintegrations to consider during shell C-burning: • 13N(γ,p)12C* • 17F(γ,p)16O* • 17O(γ,n)16O • 21Na(γ,p)20Ne • 25Al(γ,p)24Mg* For T9 > 1.2 29P(γ,p)28Si, … * = photodisintegrations dominant on the direct reaction at 1 GK

  6. In the C Shell: Possible neutron sources: 13C(α,n)16O 17O(α,n)20Ne 18O(α,n)21Ne 21Ne(α,n)24Mg 22Ne(α,n)25Mg 25Mg(α,n)28Si 26Mg(α,n)29Si

  7. The weak s-component: summary Convective Convective Core He-burning Shell C-burning Low neutron density (~106 n/cm3) T~3-3.5 108 K Classical s-process See Lamb et al. 1977, Couch et al. 1974, Prantzos et al. 1987, Raiteri et al. 1991 ...... Peak neutron density (1011- 1012 n/cm3) T~ 1 109 K The convective shell works over the ashes of the core He-burning (Raiteri et al. 1991) The final weak s component is an overposition of two different s(s+) components

  8. Models: Hydrostatic nucleosynthesis in massive stars • Post-processing models follow: Convective core He-burning and Convective shell C-burning (Raiteri et al. 1991, 1993) • Updated network Bao et al. 2000 for (n,γ) + more recent measures (KADoNiS, I. Dillmann poster), β decay rates from various sources, (n,p) and (n,α) channels....

  9. 25 Msun [Fe/H] = 0 C shell He core

  10. 25 Msun [Fe/H] = 0

  11. Z 9.4h 78.3h 68.3m 69 21.15m 71 Ga Zn 9.13h 38.1m 64 244d 66 67 68 56m 70 Cu 3.4h 9.74m 63 12.70h 65 5.1m 61.9h Ni 60 61 62 100a 64 2.52h 54.6h 59 5.72a 1.65h Co 58 45.1d 1.5e6a 6.0 m Fe A

  12. Z Rb 85 87 4.58h 6.3h 86.2d 32.8d 18.7d 17.8m 15.2m 2.6m 4.48h 10.76a 80 82 83 84 86 Kr 2.1e5a 76.3m 2.84h 3.18m 79 81 Br 17.6m 35.34h 2.40h 31.8m Se 78 80 82 6.5e4a 18m 22.4m A

  13. This is not a classic s-process!

  14. Metallicity dependence of the Weak s-process Weaver & Woosley 1995 ApJ Chieffi & Limongi 2004 ApJ

  15. He core: 22Ne (secondary-like) is the neutron source 25Mg (secondary-like) is the main neutron poison → constant neutron exposure at different metallicities constant number of neutrons captured per iron seed nc = Σ56209(A-56)[Nfin(A)-Nin(A)]/56Feini → S-PROCESS YIELDS BEYOND IRON SCALES WITH THE METALLICITY

  16. C shell: 22Ne (secondary-like) is the main neutron source 25Mg (secondary-like) and 16O, 23Na, 24Mg, 28Si…. (primary-like) are the main neutron poisons! → constant neutron exposure at different metallicities constant neutrons captured per Iron seed → S-PROCESS YIELDS BEYOND IRON SCALES WITH THE METALLICITY NO NO

  17. 25 Msun [Fe/H] = 0, -1 (He core) [Fe/H] = 0 [Fe/H] = -1

  18. 25 Msun [Fe/H] = 0, -1 (C shell) [Fe/H] = 0 [Fe/H] = -1

  19. 25 Msun [Fe/H] = 0 C shell He core

  20. 25 Msun [Fe/H] = -1

  21. Any confirmation from spectroscopic observations? YES….copper! -Bisterzo et al. 2004, NPhA

  22. Ge Abundances in Halo Stars(slide courtesy of John Cowan) Ge Fe Challenge to theorists. What happens at higher [Fe/H] with the s-process? JC et al. (2005) [A/B] = log10(A/B)star - log10(A/B)sun

  23. Summary • The Weak s-process is not ... weak • Convective C shell contribution is important for the Weak s-process • The s-process in the He core is secondary-like. This is not true any more in the C shell. • There are spectroscopic observations confirming that the Weak s-process is secondary-like at metallicities lower than solar

  24. …..and • R. Gallino and C. Baldovin (Universita’ di Torino) • M. Wiescher (University of Notre Dame) • F. Herwig and A. Heger (LANL) • M. Heil and F. Käppeler (FZK Karlsruhe)

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