The Hamburg/ESO R-process enhanced star survey (HERES). V. Detailed abundance analysis of the r-process enhanced star HE 2327-5642
Abstract
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 ion{Fe}{i} and ion{Fe}{ii}, and ion{Ca}{i} and ion{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 4.3 years.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 2010
- DOI:
- 10.1051/0004-6361/200913825
- arXiv:
- arXiv:1003.3571
- Bibcode:
- 2010A&A...516A..46M
- Keywords:
-
- stars: abundances;
- stars: atmospheres;
- stars: fundamental parameters;
- nuclear reactions;
- nucleosynthesis;
- abundances;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 16 pages, 12 figures, accepted to A&