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High resolution study of the abundance pattern of the heavy elements in very metal-poor field stars.

By Monique Spite and François Spite


9 pagesThe abundances of heavy elements in EMP stars are not well explained by the simple view of an initial basic "rapid" process. In a careful and homogeneous analysis of the "First stars" sample (eighty per cent of the stars have a metallicity [Fe/H]=-3.1±0.4), it has been shown that at this metallicity [Eu/Ba] is constant, and therefore the Eu-rich stars (generally called "r-rich") are also Ba-rich. The very large variation of [Ba/Fe] (existence of "r-poor" and "r-rich" stars) induces that the early matter was not perfectly mixed. On the other hand, the distribution of the values of [Sr/Ba] vs. [Ba/Fe] appears with well defined upper and lower envelopes. No star was found with [Sr/Ba]<-0.5 and the scatter of [Sr/Ba] increases regularly when [Ba/Fe] decreases. To explain this behavior, we suggest that an early "additional" process forming mainly first peak elements would affect the initial composition of the matter. For a same quantity of accreted matter, this additional Sr production would barely affect the r-rich matter (which already contains an important quantity of Sr) but would change significantly the composition of the r-poor matter. The abundances found in the CEMP-rs stars reflect the transfer of heavy elements from a defunct AGB companion. But the abundances of the heavy elements in CEMP-no stars present the same characteristics as the the abundances in the EMP stars

Topics: Galaxy: abundances, Galaxy: evolution, Nucleosynthesis, [ SDU.ASTR.SR ] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], [ PHYS.ASTR.SR ] Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], [ SDU.ASTR.GA ] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA], [ PHYS.ASTR.GA ] Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA]
Publisher: HAL CCSD
Year: 2013
OAI identifier: oai:HAL:hal-00871128v1
Provided by: Hal-Diderot

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