在两颗贫金属恒星中发现砷、硒和其他重元素
New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-Poor Stars
摘要：
我们使用哈勃太空望远镜上的太空望远镜成像光谱仪获得了两颗贫金属恒星HD 108317和HD 128279的新的高质量光谱，覆盖了1900到2360埃的波长范围。我们推导出丰富的Cu II，Zn II，As I，Se I，Mo II和Cd II，这是以前没有在任何一颗恒星中检测到的。Ge I，Te I，Os II和Pt I的丰度证实了来自较长波长的线的丰度。我们还从未检测到W II、Hg II、Pb II和Bi I得出上限。这两颗恒星和文献中其他五颗恒星的平均[As/Fe]比在金属丰度范围-2.8 < [Fe/H] <-0.6，<[As/Fe]> = +0.28 +/- 0.14（标准）内没有变化。dev. = 0.36 dex）。从这两颗恒星和文献中其他六颗恒星得到的平均[Se/Fe]比也是恒定的，<[Se/Fe]> = +0.16 +/- 0.09（标准）。dev. = 0.26 dex）。As和Se的丰度相对于铁峰丰度简单外推到更高的质量而增加，这表明该质量区域（75 < A < 82）可能是不同的核合成机制开始主导铁峰的准平衡富α冻结的点。HD 108317和HD 128279的<[Cu Ⅱ/Cu Ⅰ]> = +0.56 +/-0.23，推测Cu Ⅰ谱线可能不是在局部热力学平衡中形成的。[Zn/Fe]、[Mo/Fe]、[Cd/Fe]和[Os/Fe]的比值也来自中性和离子化物种，并且每个比值对在相互不确定度范围内一致，其范围为0.15至0.52 dex。
英文摘要：
We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 to 2360 Angstrom wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range -2.8 < [Fe/H] < -0.6, <[As/Fe]> = +0.28 +/- 0.14 (std. dev. = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, <[Se/Fe]> = +0.16 +/- 0.09 (std. dev. = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 < A < 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium alpha-rich freezeout of the iron peak. <[CuII/CuI]> = +0.56 +/- 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.
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