Abundance Patterns in Extremely Metal-Poor Stars

点击翻译按钮获取中文摘要

" Abundance Patterns in Extremely Metal-Poor Stars"AST- 0098617For the first time in history there is an adequate sample of stars to use as probes in deciphering the initial phases of galactic evolution. Surveys for extremely metal-poor stars, carried out in the 1990s, produced this sample. During this period of the present award, large telescopes their spectrographs will be used to determine accurate chemical abundances and thus to trace how heavy element synthesis has proceeded since earliest times. There will be additional benefits. Thorium abundances can be used to compute radiogenic ages for the oldest stars, which will put a lower limit on the age of the universe. The different contributions of s-process elements (generated in the interiors of evolving stars) and r-process elements (contributed by supernovae explosions of earlier generations of massive stars) will be assessed and compared with expectations from nucleosynthesis theory. A search will be made for Population III stars that are predicted to show extreme carbon enhancements without accompanying s-process excesses. Observations will also be made of stars belonging to galactic globular clusters in the outer halo and of stars in nearby dwarf galaxies to search for possible abundance signatures characteristic of chemical evolution in low-mass galaxies.