The origin of heavy elements in the solar system
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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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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 !


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


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


Typical conditions (Raiteri et al. ApJ367 (1991) 228 and ApJ371(1991)665:

*) time integrated neutron flux

Results:

produced abundance/solar


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)


H/He burning in a TP-AGB star

75k years

H-shell burning

(convective envelope)

CO core

He shell

From R. Gallino


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


Conditions during the main s-process

short, intense burstslight modificationof abundances(branchings !)

weaker but longermain contribution(90% of exposure)


Results for main s-process model

= s-only

(Arlandini et al. ApJ525 (1999) 886)


SiC (IRAS)

Of an AGB star

Lab spectrum

But: can vary C excess,can have other contaminantsin star (diamonds …)

Grains from AGB stars


Murchison CM chondrite


Zr in the s-process

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


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


d(90Zr/94Zr)

d(91Zr/94Zr)

d(92Zr/94Zr)

Lugaro et al., 2003, ApJ


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