The S-process in Metal-poor Stars: Abundances for 22 Neutron-capture Elements in Cs 31062-050

The CH star CS 31062-050 ([Fe/H] = −2.42) is one of the most useful stars yet discovered for evaluating the s-process in metal-poor stars. It is very abundant in heavy elements (e.g., [La/Fe] = 2.2), and its relatively cool temperature and low gravity mean that there are many lines of interesting elements present in the spectrum. We measured the abundances of 22 elements with Z≥29, including the rarely measured Lu and Pd. We derive an upper limit on the Th abundance as well. The abundances in CS 31062-050 show a similar pattern to many other metal-poor CH stars: high [Pb/Fe] and [Pb/La] ratios, low [Y/La] ratios and high [Eu/La] values compared to the solar system s-process. However, the Th limit, with additional assumptions, is not consistent with the idea that the excess Eu in CS 31062-050 is contributed by the r-process. In addition, the observed [Eu/Tb] cannot be explained by any ratio of solar-system s-process and r-process abundances. We therefore argue that the abundance pattern in CS 31062-050 is most likely the result of the s-process, and we discuss possible modifications that could explain the non-solar-system pattern observed. Subject headings: nuclear reactions, nucleosynthesis, abundances, stars:abundances — stars: atmospheres — stars: Population II