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| Paper: |
Chemistry Of Extremely Metal-Poor Halo Stars |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
317 |
| Authors: |
McWilliam, Andrew; Preston, George; Sneden, Christopher; Searle, Leonard; Shectman, Stephen |
| Abstract: |
We present the results of an abundance study of 33 extremely metal-poor stars (-4.0<= [Fe/H]<= -2.0). For Cr, Mn, and Co we identify previously unnoticed trends of abundance with [Fe/H]. These results demonstrate that there must be a large range of iron-peak nucleosynthesis yields from type II supernovae (SN), and that there was a systematic change in the mixture of SN subtypes with increasing metallicity. These findings, and the trends of other elements, suggest that our stars were born at a time when nucleosynthesis was very different than during the later epoch of the globular clusters. The heavy metal abundances in our stars are in excellent agreement with the solar system r-process pattern. We find considerable star to star scatter of the r-process abundance relative to [Fe/H] (e.g. we find ~ 300 range in the Ba/Fe ratio at a fixed [Fe/H]). This observations sets a lower limit to the range of r-process yields from type II SN. We also find one star with iron-peak abundances depressed by ~ 1 dex, relative to lighter and heavier elements. The observed abundance dispersions suggest that at low metallicity the Galaxy was not very homogeneous, due to insufficient time for mixing, and due to variable element yields from the small number of type II SN which had occurred. |
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