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| Paper: |
Can the Main Component of the s-Process in AGB Stars
Constrain the 13C-Pocket Formation? |
| Volume: |
497, Why Galaxies Care about AGB Stars III: A Closer Look in Space and Time |
| Page: |
275 |
| Authors: |
Trippella, O.; Busso, M.; Maiorca, E.; Käppeler, F.; Palmerini, S. |
| Abstract: |
The s-process main component is mainly produced in low-mass AGB stars
by the 13C(α,n)16O reaction, requiring
proton injection from the envelope. The 13C pocket was
typically assumed to involve a small mass (≤ 10–3M☉) (Gallino et al. 1998), but models with rotation suggest that 14N
hampers s-processing in such tiny layers. Recent spectroscopy of
young open clusters, showing enhancements of s-element abundances
with respect to the Sun, have indicated a more effective s-process
production requiring 13C-rich layers extended in mass
(≥4 ×10–3M☉). We speculated that mixing
driven by magnetic buoyancy (as in Maiorca et al. 2012; Trippell et al. 2014, or other forced mechanisms "from the bottom to top')
can form a 13C reservoir larger than assumed so far,
covering most of the He-rich layers. We present new calculations (Tripella et al. 2014) aimed at understanding if the solar composition helps
to constrain the 13C-pocket extension. Stellar models at a
fixed metallicity, based on a large 13C reservoir, reproduce
the main s-component as accurately as before and don't require any
nuclear contribution from an unknown nucleosynthesis processes (LEPP).
These models also avoid problems of mixing at the envelope border and
meet requirements from C-star luminosities. A large production of nuclei
below A=90 is expected, so that 86,87Sr may be fully
synthesized by AGB stars, while 88Sr, 89Y and
94Zr are contributed more efficiently than before. |
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