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 ( \mathrm { [ Fe / H ] } = -2.51 , \mathrm { [ r / Fe ] } = +1.1 ) and HE~1219 $ - $ 0312 ( \mathrm { [ Fe / H ] } = -2.96 , \mathrm { [ 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 Å 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 ” .