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

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 origin of heavy elements in the solar system

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 origin of heavy elements in the solar system

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


The origin of heavy elements in the solar system

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

*) time integrated neutron flux

Results:

produced abundance/solar


The origin of heavy elements in the solar system

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)


The origin of heavy elements in the solar system

H/He burning in a TP-AGB star

75k years

H-shell burning

(convective envelope)

CO core

He shell

From R. Gallino


The origin of heavy elements in the solar system

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


The origin of heavy elements in the solar system

Conditions during the main s-process

short, intense burstslight modificationof abundances(branchings !)

weaker but longermain contribution(90% of exposure)


The origin of heavy elements in the solar system

Results for main s-process model

= s-only

(Arlandini et al. ApJ525 (1999) 886)


The origin of heavy elements in the solar system

SiC (IRAS)

Of an AGB star

Lab spectrum

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

Grains from AGB stars


The origin of heavy elements in the solar system

Murchison CM chondrite


The origin of heavy elements in the solar system

Zr in the s-process

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


The origin of heavy elements in the solar system

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


The origin of heavy elements in the solar system

d(90Zr/94Zr)

d(91Zr/94Zr)

d(92Zr/94Zr)

Lugaro et al., 2003, ApJ


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