The Hamburg/ESO R-process enhanced star survey (HERES). V. Detailed abundance analysis of the r-process enhanced star HE 2327-5642
The Hamburg/ESO R-process enhanced star survey (HERES). V. Detailed abundance analysis of the r-process enhanced star HE 2327-5642
复制标题
DOI：
10.1051/0004-6361/200913825
复制
发表时间：
2010-03
影响因子：
6.5
通讯作者：
L. Mashonkina;N. Christlieb;P. Barklem;V. Hill;T. Beers;A. Velichko
中科院分区：
文献类型：
--
作者：
L. Mashonkina;N. Christlieb;P. Barklem;V. Hill;T. Beers;A. Velichko
目标。本文对HERES项目HE 2327-5642中发现的一颗强r过程增强星星进行了详细的丰度分析，其[Fe/H] =-2.78，[r/Fe] =+0.99。方法.通过分析高质量的VLT/UVES光谱，确定了恒星的参数和元素丰度。根据Fe I和Fe II以及Ca I和Ca II之间的非局部热力学平衡（NLTE）电离平衡计算表面重力。结果在HE 2327-5642中确定了总共40种元素和23种超过Sr和Th的中子捕获元素的精确丰度。对于每一种化学物质，单线测量值在平均值附近的离散度不超过0.11 dex。HE 2327-5642的重元素丰度模式与先前从其他强r过程增强星（如CS 22892-052、CS 31082-001和HE 1219-0312）得到的结果非常一致。从Ba到Hf范围内的元素与比例太阳能r过程模式非常匹配。由于太阳r过程的不确定性，关于HE 2327-5642中的第一个中子俘获峰元素Sr到Pd与太阳r过程之间的关系，还不能得出确切的结论。不同铕增强晕星的Sr/Eu丰度比有明显的差别。强r过程增强星的Sr/Eu丰度比较低，为-0.92 +/-0.13，而0 < [Eu/Fe] < 1和[Eu/Fe] < 0的星的Sr/Eu值分别高出0.36 dex和0.93 dex。用钍和稀土元素丰度对HE 2327-5642进行放射性测年，得到的平均年龄为13.3 Gyr（基于高熵风计算）和5.9 Gyr（使用太阳r残差）。我们建议，HE 2327-5642是一个径向速度变量的基础上，我们的高分辨率光谱覆盖类似于4.3年。
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.