2006ApJ...636..842W -
Astrophys. J., 636, 842-847 (2006/January-2)
Enrichment of very metal poor stars with both R-process and S-process elements from 8-10 M☉stars.
WANAJO S., NOMOTO K., IWAMOTO N., ISHIMARU Y. and BEERS T.C.
Abstract (from CDS):
Recent spectroscopic studies have revealed the presence of numerous carbon-enhanced, metal-poor stars with [Fe/H]←2.0 that exhibit strong enhancements of s-process elements. These stars are believed to be the result of a binary mass transfer episode from a former asymptotic giant branch (AGB) companion that underwent s-process nucleosynthesis. However, several such stars exhibit significantly lower Ba/Eu ratios than solar s-process values. This might be explained if there were an additional contribution from the r-process, thereby diluting the Ba/Eu ratio by extra production of Eu. We propose a model in which the double enhancements of r-process and s-process elements originate from a former 8-10 M☉ companion in a wide binary system, which may undergo s-processing during an AGB phase, followed by r-processing during its subsequent supernova explosion. The mass of Eu (as representative of r-process elements) captured by the secondary through the wind from the supernova is estimated and is assumed to be proportional to the geometric fraction of the secondary (low-mass, main-sequence) star with respect to the primary (exploding) star. We find that the estimated mass is in good agreement with a constraint on the Eu yield per supernova event obtained from a Galactic chemical evolution study, when the initial orbital separation is taken to be ∼1 yr. If one assumes an orbital period on the order of 5 yr, the efficiency of wind pollution from the supernova must be enhanced by a factor of ∼10. This may, in fact, be realized if the expansion velocity of the supernova's innermost ejecta, in which the r-process has taken place, is significantly slow, resulting in an enhancement of accretion efficiency by gravitational focusing.
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Journal keyword(s):
Galaxy: Evolution - Galaxy: Halo - Nuclear Reactions, Nucleosynthesis, Abundances - Stars: Abundances - Stars: Population II - Stars: Supernovae: General
Simbad objects:
11
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