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
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
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DOI：
10.1051/0004-6361/200811121
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发表时间：
2009-09
影响因子：
6.5
通讯作者：
Wolfgang Hayek;Wolfgang Hayek;U. Wiesendahl;N. Christlieb;Kjell Eriksson;A. Korn;P. Barklem;
中科院分区：
文献类型：
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作者：
Wolfgang Hayek;Wolfgang Hayek;U. Wiesendahl;N. Christlieb;Kjell Eriksson;A. Korn;P. Barklem;
我们报告了在HERES计划中新发现的两颗强r过程增强的、非常贫金属的恒星的详细丰度分析，CS 29491−069([Fe/H]=−2.51，[r/Fe]=+1.1)和HE1219−0312([Fe/H]=−2.96，[r/Fe]=+1.5)。分析基于高质量的VLT/UVES光谱和MARCS模式大气。我们在CS 29491−069的光谱中检测到15个重元素的谱线，在HE 1219−0312中检测到18个重元素的谱线；在这两种情况下，都包括Th II 4019 A谱线。这两颗恒星的重元素丰度模式大多与不是S过程形成的太阳剩余丰度的比例很好地匹配。我们还将观测到的模式与最近的高熵风(HEW)计算进行了比较，后者假设大质量恒星的核心塌缩超新星为r过程的天体物理环境，并发现对大多数稀土元素都有很好的一致性。该模型很好地再现了轻元素锶、钇和锆的丰度比，这些元素可能不是由主要的r过程形成的。用观测到的钍和稀土元素丰度对对CS 29491−069进行放射性测年，根据太阳r过程残差计算的平均年龄为9.5Gyr，使用HEW模型预测的平均年龄为17.6Gyr。在HE1219−0312的情况下，比色法似乎失败了，由于其高的钍丰度，导致了负年龄。因此，1219年−0312可能会显示出过多的最重元素，这有时被称为“鳗系元素加速”。
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 Th II 4019 A 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”.