Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA.
Nature. 2010 Mar 4;464(7285):72-5. doi: 10.1038/nature08772.
Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.
目前的宇宙学模型表明，银河系的恒星晕是由许多较小的系统组装而成的。基于目前矮星系中最贫金属恒星的明显缺失，最近的研究声称，真正的银河构建块一定与幸存的矮星系有很大的不同。根据中分辨率光谱在 Sculptor 矮星系中发现一颗极其贫铁恒星（S1020549），对这一结论提出了一些质疑。然而，要证明是同类型的恒星产生了在矮星系和银河晕中发现的金属，就必须验证铁的缺乏，并测量其他元素，如 α 元素 Mg。只有这样，才能最终将矮星系恒星与早期恒星晕的组装联系起来。在这里，我们报告了 S1020549 中 11 种元素的高分辨率光谱丰度，证实其铁丰度不到太阳的 1/4000，并表明其整体丰度模式与低金属丰度晕星中的丰度模式一致，包括 α 元素。这种化学相似性表明，数十亿年前形成晕的系统与当今矮星系的前身并没有本质上的不同，这表明所有星系的早期化学富集可能几乎是相同的。
