Spectroscopic Studies of Very Metal-poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements

By Wak Aoki, Satoshi Honda, Timothy C. Beers, Toshitaka Kajino, H. Ando, J. Norris, S. Ryan, H. Izumiura, K. Sadakane, M. Takada-Hidai. 2005

158 citations recorded by the source corpus.

Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1 ≲ [Fe/H] ≲ -2.4. The abundances of carbon, α-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large overabundance of Mg, Al, and Sc found in BS 16934-002, a giant with [Fe/H] = -2.8. Interestingly, this is the most metal-rich star (by about 1 dex in [Fe/H]) known with such large overabundances in these elements. Furthermore, BS 16934-002 does not share the large overabundances of carbon that are associated with the two other, otherwise similar, extremely metal-poor stars CS 22949-037 and CS 29498-043. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr). Large scatter is found in the abundance ratios between the light and heavy neutron-capture elements (e.g., Sr/Ba, Y/Eu) for stars with low abundances of heavy neutron-capture elements. Most of these stars have extremely low metallicity ([Fe/H] ≲ -3). By contrast, the observed scatter in these ratios is much smaller in stars with excesses of heavy neutron-capture elements and with higher metallicity. These results can be naturally explained by assuming that two processes independently enriched the neutron-capture elements in the early Galaxy. One process increases both light and heavy neutron-capture elements and affects stars with [Fe/H] ≳ -3, while the other process contributes only to the light neutron-capture elements and affects most stars with [Fe/H] ≳ -3.5. Interestingly, the Y/Zr ratio is similar in stars with high and low abundances of heavy neutron-capture elements. These results provide constraints on modeling of neutron-capture processes, in particular, those responsible for the nucleosynthesis of light neutron-capture elements at very low metallicity.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/25f207734d5ee7a812125fc28b9f28b2e5b5f61c

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In Astronomy and Astrophysics

1. Timothy C. Beers
2. C. Sneden
3. Roberto Gallino
4. A. Frebel
5. J. Cowan
6. J. Norris
7. Wak Aoki
8. N. Christlieb

In Instrumentation

1. Timothy C. Beers
2. A. Frebel
3. C. Sneden
4. Roberto Gallino
5. J. Norris
6. J. Cowan
7. M. Walker
8. Martin Asplund

Citations in the corpus

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• Neutron-Capture Elements in the Early Galaxy (2008, background): “Aoki et al. (2005) extend these arguments with a different stellar sample, demonstrating that the light/heavy scatter is larger in stars with smaller overall ncapture enrichment.”
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