Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy ∗
Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy ∗
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DOI：
10.1093/pasj/56.6.1041
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发表时间：
2004-11
影响因子：
2.3
通讯作者：
K. Sadakane;N. Arimoto;C. Ikuta;W. Aoki;P. Jablonka;A. Institute;O. University;Natinal Astronomical Observatory of Japan;O. Paris;Subaru Telescope
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文献类型：
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作者：
K. Sadakane;N. Arimoto;C. Ikuta;W. Aoki;P. Jablonka;A. Institute;O. University;Natinal Astronomical Observatory of Japan;O. Paris;Subaru Telescope
利用Subaru望远镜上的高色散摄谱仪（HDS）获得了小熊座矮椭球星系中3颗红巨星（COS 4，COS 82和COS 347）的高分辨率光学区光谱。这些恒星的化学丰度分析了26种元素，包括α-，铁峰和中子捕获元素。这三颗恒星的α-元素（Mg、Si和Ca）丰度都很低，其中两颗恒星（COS 82和COS 347）的Mn丰度比类似金属丰度的银河系晕星高。其中一颗星星（COS 4）被证实是非常缺乏金属的（[Fe/H] =-2.7），并且发现Mn、Cu和Ba的丰度非常低。在另一颗星星，COS 82（[Fe/H] =-1.5）中，我们发现了大量过量的重中子捕获元素，其总体丰度模式类似于缩放太阳系r过程丰度曲线。这些观测结果相当令人困惑：α元素丰度低，Mn丰度高，似乎表明在低金属丰度时，超新星Ia的贡献很大，而没有s过程的迹象（即，AGB星）的贡献，即使在[Fe/H] =-1.5，这表明UMi dSph星系有一个特殊的核合成历史。银河系矮球星系的起源与银河系的形成和演化历史密切相关。基于冷暗物质范式的现代宇宙学模型证明了所有尺度上等级结构形成的重要性。像银河系和M31这样的星系团是原始物质分布中局部密度过高的一部分，通过聚集许多较小的建筑块形成，这些建筑块可以独立发展成矮星系。在本星系群中，这一过程的残留物可以在矮星系的分布和性质中看到，矮椭球体主要靠近巨螺旋星系，而矮不规则星系则更均匀地分布在整个本星系群中。引力束缚的矮星系成功地避免了潮汐的破坏和随后的合并，它们在哈勃时间内经历了间歇性的星星形成。相对来说，富含气体的矮不规则星仍然显示出正在形成的星星，而矮球状体，由于缺乏大量的气体和尘埃，现在是静止的，因此，原则上，研究起来要简单得多。银河系dSphs的接近为研究银河系提供了一个独特的机会。
With the HDS (High Dispersion Spectrograph) on the Subaru Telescope, we obtained high-resolution optical region spectra of three red giant stars (COS 4, COS 82, and COS 347) in the Ursa Minor dwarf spheroidal galaxy. The chemical abundances in these stars were analyzed for 26 elements, including α-, iron-peak, and neutron-capture elements. All three stars show low abundances of α-elements (Mg, Si, and Ca), and two stars (COS 82 and COS 347) show high abundances of Mn compared to Galactic halo stars of similar metallicity. One star (COS 4) has been confirmed to be very metal deficient ([Fe/H] = −2.7) and found to show anomalously low abundances of Mn, Cu, and Ba. In another star, COS 82 ([Fe/H] = −1.5), we have found a large excess of heavy neutron-capture elements with a general abundance pattern similar to the scaled solar system r-process abundance curve. These observational results are rather puzzling: low abundances of α-elements and high abundance of Mn seem to suggest a significant contribution of SNe Ia at low metallicity, while there is no hint of an s-process (i.e., AGB stars) contribution, even at [Fe/H] = −1.5, suggesting a peculiar nucleosynthetic history of the UMi dSph galaxy. The origin of the Galactic dwarf spheroidal (dSph) galaxies is closely related to the formation and evolutionary history of the Milky Way. Modern cosmological models based on the Cold Dark Matter paradigm demonstrate the importance of hierarchical structure formation on all scales. Galaxies like the Milky Way and M31 form as part of a local overdensity in the primordial matter distribution via the agglomeration of numerous smaller building blocks that can independently develop into dwarf galaxies. In the Local Group the leftovers of this process are seen in the distribution and properties of the dwarf galaxies, with the dwarf spheroidals found mainly close in to the giant spirals, while the dwarf irregulars are more evenly distributed throughout the Local Group. The gravitationally bound dwarf galaxies that have managed to avoid tidal destruction and subsequent merging have undergone episodic star formation over a Hubble time. The relatively gas-rich dwarf irregulars still exhibit ongoing star formation, while the dwarf spheroidals, being devoid of significant amounts of gas and dust, are now quiescent, and are therefore, in principle, much simpler systems to study. The proximity of the Galactic dSphs offers a unique opportunity for investigating ∗ Based on data collected at the Subaru Telescope, which is operated by the