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The origin of heavy elements in the solar system

The origin of heavy elements in the solar system. Location of peaks indicates n-capture along valley of stability  s-process. s-only isotopes are above p-process level  s-process. (Pagel, Fig 6.8). each process contribution is a mix of many events !. The sites of the s-process.

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The origin of heavy elements in the solar system

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  1. The origin of heavy elements in the solar system Location of peaksindicates n-capture along valley of stability  s-process s-only isotopesare above p-processlevel  s-process (Pagel, Fig 6.8) each process contribution is a mix of many events !

  2. The sites of the s-process weak s-process: core He/ shell C burning in massive stars main s-process: He shell flashes in low mass TP-AGB stars approx. steady flow can easily interpolates-contribution for s+r-nucleiif neutron capture crosssections are known

  3. The weak s-process Site: Core He burning (and shell C-burning) in massive stars (e.g. 25 solar masses) 14N is rapidly converted to 22Ne 22Ne He burning corecontainsinitially 14N a capture 18F b+ a capture 18O 14N Towards the end of He burning T~3e8 K: 22Ne(a,n) provides a neutron source preexisting Fe (and other nuclei) serve as seed for a (secondary) s-process

  4. Typical conditions (Raiteri et al. ApJ367 (1991) 228 and ApJ371(1991)665: *) time integrated neutron flux Results: produced abundance/solar

  5. The main s-process Site: low mass TP-AGB stars ( thermally pulsing stars on the asymptotic giant branch in the HR diagram, 1.5 - 3 solar masses ) H-burning shell CO core He-burning shell unstable - burns in flashes(thin shell instability)

  6. H/He burning in a TP-AGB star 75k years H-shell burning (convective envelope) CO core He shell From R. Gallino

  7. H/He burning in a TP-AGB star • number of He flashes in stars life: few – 100 • period of flashes: 1000 – 100,000 years 13C(a,n) Transport of s-process products to the surface 22Ne(a,n) s-process in: • He flash via 22Ne(a,n) • 13C pocket via 13C(a,n) 13C pocket formation by mixingHe burning products with Hvia 12C + p  13N  13C

  8. Conditions during the main s-process short, intense burstslight modificationof abundances(branchings !) weaker but longermain contribution(90% of exposure)

  9. Results for main s-process model = s-only (Arlandini et al. ApJ525 (1999) 886)

  10. SiC (IRAS) Of an AGB star Lab spectrum But: can vary C excess,can have other contaminantsin star (diamonds …) Grains from AGB stars

  11. Murchison CM chondrite

  12. Zr in the s-process Even this can have s-contribution(for large Nn and slow 96Zr(n,g) helps – maybe 50% s?)

  13. Definition: d(X/Y)=[ (X/Y) / (X/Y)sol -1] x 103 d(90Zr/94Zr) d(91Zr/94Zr) d(92Zr/94Zr) (D=divide, U=multiply amount of 13C formed = pocket efficiency) Lugaro et al., 2003, ApJ

  14. d(90Zr/94Zr) d(91Zr/94Zr) d(92Zr/94Zr) Lugaro et al., 2003, ApJ

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