期刊
ASTRONOMY & ASTROPHYSICS
卷 504, 期 2, 页码 511-U261出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200811121
关键词
stars: abundances; nuclear reactions, nucleosynthesis, abundances; Galaxy: halo; Galaxy: abundances; Galaxy: evolution
资金
- Deutsche Forschungsgemeinschaft [Ch 214/3, Re 353/44, KR 806/13-1]
- Knut and Alice Wallenberg Foundation
- Swedish Research Council
- US National Science Foundation [AST 07-07776]
- Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) [PHY 02-16783, PHY 08-22648]
- Helmholtz-Gemeinschaft [VH-VI-061]
We report on a detailed abundance analysis of two strongly r-process enhanced, very metal-poor stars newly discovered in the HERES project, CS 29491-069 ([Fe/H] = -2.51, [r/Fe] = +1.1) and HE 1219-0312 ([Fe/H] = -2.96, [r/Fe] = +1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS 29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 angstrom line. The heavy-element abundance patterns of these two stars are mostly well-matched to scaled solar residual abundances not formed by the s-process. We also compare the observed pattern with recent high-entropy wind (HEW) calculations, which assume core-collapse supernovae of massive stars as the astrophysical environment for the r-process, and find good agreement for most lanthanides. The abundance ratios of the lighter elements strontium, yttrium, and zirconium, which are presumably not formed by the main r-process, are reproduced well by the model. Radioactive dating for CS 29491-069 with the observed thorium and rare-earth element abundance pairs results in an average age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when using HEW model predictions. Chronometry seems to fail in the case of HE 1219-0312, resulting in a negative age due to its high thorium abundance. HE 1219-0312 could therefore exhibit an overabundance of the heaviest elements, which is sometimes called an actinide boost.
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