2009A&A...504..511H -
Astronomy and Astrophysics, volume 504, 511-524 (2009/9-3)
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.
HAYEK W., WIESENDAHL U., CHRISTLIEB N., ERIKSSON K., KORN A.J., BARKLEM P.S., HILL V., BEERS T.C., FAROUQI K., PFEIFFER B. and KRATZ K.-L.
Abstract (from CDS):
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 ThII 4019Å 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 9.5Gyr, when based on solar r-process residuals, and 17.6Gyr, 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''.
Abstract Copyright:
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Journal keyword(s):
stars: abundances - nuclear reactions, nucleosynthesis, abundances - Galaxy: halo - Galaxy: abundances - Galaxy: evolution
Simbad objects:
10
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