Halo Star Abundance Signatures with Improved Atomic Data: Evidence of Early Galactic Nucleosynthesis

Details Halo Star Abundance Signatures with Improved Atomic Data: Evidence of Early Galactic Nucleosynthesis Halo Star Abundance Signatures with Improved Atomic Data: Evidence of Early Galactic Nucleosynthesis

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21113108c&link_type=abstract

American Astronomical Society, AAS Meeting #211, #131.08; Bulletin of the American Astronomical Society, Vol. 39, p.960

Astronomy and Astrophysics

Astronomy

Scientific paper

Many Galactic halo field and globular cluster stars are enriched in neutron-capture (i.e., s- and r-process) elements. Accurate abundance determinations of these elements depend critically upon reliable atomic data, and improved laboratory transition probabilities are now in hand for the majority of observable n-capture elements. We have now utilized these new atomic data to obtain updated and more reliable determinations of the abundances of these elements in metal-poor Galactic halo stars. These newly determined stellar abundances in the r-process-rich halo stars indicate that the heaviest neutron-capture elements (i.e., Ba and above) are consistent with a scaled solar system r-process (only) abundance distribution, while the lighter such elements do not conform to the solar pattern.
These comparisons suggest the possibility of two r-process sites in stars. Metal-poor star observations also provide insight into early Galactic nucleosynthesis and the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis. In particular a large star-to-star scatter is observed in the abundances of neutron-capture element/iron, but not Mg/Fe, ratios at low metallicities. This scatter, which disappears with increasing metallicity or [Fe/H], suggests different environments for the syntheses of these elements and that the formation of the neutron-capture elements (presumably from certain types of supernovae) was rare in the early Galaxy.
The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution.
This work has been supported in part by the National Science Foundation through grants AST-0707447 to JJC, AST-0607708 to CS and AST-0506324 to JEL and EADH.

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