The Hamburg/ESO R-process enhanced star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312

• Published in: Astronomy and astrophysics (Berlin) Vol. 504; no. 2; pp. 511 - 524
• Main Authors: HAYEK, W, WIESENDAHL, U, KRATZ, K.-L, CHRISTLIEB, N, ERIKSSON, K, KORN, A. J, BARKLEM, P. S, HILL, V, BEERS, T. C, FAROUQI, K, PFEIFFER, B
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.09.2009
• Subjects: abundances; Astronomy; Earth, ocean, space; Exact sciences and technology; Fysik; Galaxy: abundances; Galaxy: evolution; Galaxy: halo; NATURAL SCIENCES; NATURVETENSKAP; nuclear reactions; nucleosynthesis; Physics; stars: abundances; Collapse; Galaxy evolution; Galaxy halo; nuclear reactions, nucleosynthesis, abundances; Galaxies; Atmosphere model; Supernovae; Nucleosynthesis; Galaxy: evolution; Stellar abundance; Entropy; r process; stars: abundances; Massive stars; Heavy element; Galaxy: halo; Solar abundance; s process; Element abundance; Galaxy: abundances; Abundance ratio; Age; Metal-poor stars
• ISSN: 0004-6361; 1432-0746; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/200811121

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".