Neutron capture elements

Abundance results for additional clusters are currently underway and include analyses of the neutron-capture elements (in order to trace the onset of contributions from low-mass Type II SNe as well as AGB stars). Combined with their ages, the nucleosynthetic histories of the outer halo clusters will better constrain the timescales of formation and construction of the Galaxy. 

These setups have been chosen to measure abundances of iron peak, a-elements and neutron-capture elements. In parallel, a subset of 14 stars has been observed with the high resolution spectrograph UVES (R=48000) to serve as calibrators for the GIRAFFE sample. 

Abstract. Observed large scatters in abundances of neutron-capture elements in metal-poor stars suggest that they are enriched a single or a few supernovae. Comparing predictions by an inhomogeneous chemical evolution model and new observational results with Subaru HDS, we attempt to constrain the origins of r-process elements. 

The Galactic chemical evolution of heavy neutron-capture elements was studied by Travaglio et al. (1999, 2001) on the assumption that a small pocket of 13C is mixed into the inter-shell zone after the decay of each thermal pulse and generates neutrons supplemented by a small contribution from 22Ne during the next pulse see... 

Sneden C. (2001) Neutron-capture element abundances and cosmochronometry. CERN Document Server astro-ph/0106366. 

Two dominant themes run throughout the evolution of late type star compositions the abundances of the isotopes of carbon, nitrogen, and oxygen, and the abundances of the metals heavier than the iron peak - the neutron capture elements usually associated with the s-process. In addition to these elements, the abundance of lithium can also be a distinguishing characteristic of some groups, and can be used to interpret possible origins for some of these peculiar stars. 

Intermediate-mass red giant stars are understood to be the primary source both of and of the heavy s-process (slow neutron capture) elements, as well as a significant source of and other less abundant CNO isotopes. Their contributions to galactic nucleosynthesis are... 

It is generally accepted that the r-process synthesis of the heavy neutron capture elements in the mass regime A S 130-140 occurs in an environment associated with massive stars. This results from two factors (i) the two most promising mechanisms for r-process synthesis—a neutrino heated hot bubble and neutron star mergers— are both tied to environments associated with core collapse supernovae and (ii) observations of old stars (discussed in Section 1.01.6) confirm the early entry of r-process isotopes into galactic matter. 

Burris D. L., Pilachowski C. A., Armandroff T. A., Sneden C., Cowan J. J., and Roe H. (2000) Neutron-capture elements in the early galaxy insights from a large sample of metal-poor giants. Astrophys. J. 544, 302-319. 

Gratton R. G. and Sneden C. (1994) Abundances of neutron-capture elements in metal-poor stars. Astron. Astrophys. 287, 927-946. 

Ba/Eu] is low in halo stars, indicating that the s-process (which is the main source of Ba) has not had sufficient time to contribute to the abundances in halo stars, while the r-process (the main source of Eu) dominates in metal-poor stars. Indeed, very metal-poor halo giants show evidence for a purely r-process contribution to the abundances of heavy neutron capture elements (Sneden et al. 2000). 

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