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

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".

Wiesendahl, U (författare)
Christlieb, N (författare)
Eriksson, KUppsala universitet,Institutionen för fysik och astronomi(Swepub:uu)kjelerik (författare)
Korn, A. J.Uppsala universitet,Institutionen för fysik och astronomi (författare)
Barklem, P. S.Uppsala universitet,Institutionen för fysik och astronomi (författare)
Hill, V (författare)
Beers, C (författare)
Farouqi, K (författare)
Pfeiffer, B (författare)
Kratz, K.-L. (författare)
Uppsala universitetInstitutionen för fysik och astronomi (creator_code:org_t)

Ingår i:Astronomy and Astrophysics: EDP Sciences504:2, s. 511-5240004-63611432-0746

Av författaren/redakt...: Hayek, W; Wiesendahl, U; Christlieb, N; Eriksson, K; Korn, A. J.; Barklem, P. S.; visa fler...; Hill, V; Beers, C; Farouqi, K; Pfeiffer, B; Kratz, K.-L.; visa färre...

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