Journal
ASTRONOMY & ASTROPHYSICS
Volume 516, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200913825
Keywords
stars: abundances; stars: atmospheres; stars: fundamental parameters; nuclear reactions, nucleosynthesis, abundances
Categories
Funding
- Russian Foundation for Basic Research [08-02-92203-GFEN-a]
- Russian Federal Agency on Science and Innovation [02.740.11.0247]
- Swiss National Science Foundation [IZ73Z0-128180/1]
- Knut and Alice Wallenberg Foundation
- Deutsche Forschungsgemeinschaft [Ch 214/3, Re 353/44]
- Swedish Research Council
- U.S. National Science Foundation [PHY 02-16783, PHY 08- 22648]
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Aims. We present a detailed abundance analysis of a strongly r-process enhanced giant star discovered in the HERES project, HE 2327-5642, for which [Fe/H] = -2.78, [r/Fe] = +0.99. Methods. We determined the stellar parameters and element abundances by analyzing the high-quality VLT/UVES spectra. The surface gravity was calculated from the non-local thermodynamic equilibrium (NLTE) ionization balance between Fe I and Fe II, and Ca I and Ca II. Results. Accurate abundances for a total of 40 elements and for 23 neutron-capture elements beyond Sr and up to Th were determined in HE 2327-5642. For every chemical species, the dispersion in the single line measurements around the mean does not exceed 0.11 dex. The heavy element abundance pattern of HE 2327-5642 is in excellent agreement with those previously derived for other strongly r-process enhanced stars, such as CS 22892-052, CS 31082-001, and HE 1219-0312. Elements in the range from Ba to Hf match the scaled Solar r-process pattern very well. No firm conclusion can be drawn about the relationship between the fisrt neutron-capture peak elements, Sr to Pd, in HE 2327-5642 and the Solar r-process, due to the uncertainty in the Solar r-process. A clear distinction in Sr/Eu abundance ratios was found between the halo stars of different europium enhancement. The strongly r-process enhanced stars contain a low Sr/Eu abundance ratio at [Sr/Eu] = -0.92 +/- 0.13, while the stars with 0 < [Eu/Fe] < 1 and [Eu/Fe] < 0 have 0.36 dex and 0.93 dex higher Sr/Eu values, respectively. Radioactive dating for HE 2327-5642 with the observed thorium and rare-earth element abundance pairs results in an average age of 13.3 Gyr, when based on the high-entropy wind calculations, and 5.9 Gyr, when using the Solar r-residuals. We propose that HE 2327-5642 is a radial-velocity variable based on our high-resolution spectra covering similar to 4.3 years.
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