IDENTIFYING CONTRIBUTIONS TO THE STELLAR HALO FROM ACCRETED, KICKED-OUT, AND IN SITU POPULATIONS
IDENTIFYING CONTRIBUTIONS TO THE STELLAR HALO FROM ACCRETED, KICKED-OUT, AND IN SITU POPULATIONS
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确定吸积、踢出和原位种群对恒星光环的贡献
DOI：
10.1088/0004-637x/761/2/161
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
R. Patterson
中科院分区：
文献类型：
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作者：
Allyson A. Sheffield;S. Majewski;K. Johnston;K. Cunha;V. Smith;Andrew M. Cheung;Christina M. Hampton;T. David;R. Wagner;Marshall C. Johnson;Evan Kaplan;Jacob H. Miller;R. Patterson
我们对银河系中纬度 (30° < |b| < 60°) 的晚型巨星进行了中分辨率光谱调查，旨在探测距离为 ∼9 kpc 的该星群的特性。由于 M 巨星通常富含金属，而且我们通过纬度选择限制了薄盘恒星的污染，因此调查中的大多数恒星预计都是厚盘 (<[Fe/H]> ∼ -0.6) 的成员，其中一些来自附近晕的富含金属成分的贡献。在这里，我们报告了 1799 颗星星的第一个结果。这些恒星的径向速度 (RV) 的分布与 l 的函数关系表明 (1) 预期的厚盘种群和 (2) 局部富含金属的晕恒星相对于盘高速运动，在某些情况下在 RV-l 空间中形成不同的序列。对其中 34 颗“RV 异常值”拍摄的高分辨率中阶梯光栅光谱揭示了 [Ti/Fe]-[Fe/H] 平面上的以下模式：其中 17 颗恒星的丰度让人想起银河系矮卫星中的星群，8 颗恒星的丰度与银盘和金属更丰富的光环的丰度一致，9 颗恒星落在由光环中大多数恒星定义的轨迹上。 RV 异常值的化学丰度趋势表明，该样本主要由坠落矮星系吸积的恒星组成。 RV异常样本中的一小部分恒星可能是在内星系中形成的，随后被踢到更高偏心率的轨道，但样本不够大，无法最终区分这种解释和这些恒星代表厚盘速度分布尾部的另一种解释。我们的数据并不排除少数样本可能是在当前轨道上原位由气体形成的可能性。这些结果与恒星晕至少由 M 巨星探测到的情况是一致的，它是由多种形成机制产生的。然而，从表面上看，我们对富含金属的晕巨星的结果表明，吸积的比例比卡罗洛等人的发现要高得多。更像是 Nissen & Schuster 和 Schuster 等人的分析中建议的分数。我们得出的结论是，具有大型 RV 的 M 巨星可以为挖掘吸积结构提供特别丰富的样本，并且某些速度序列可能确实对应于最近吸积事件产生的真实物理关联。
We present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30° < |b| < 60°), designed to probe the properties of this population to distances of ∼9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk (〈[Fe/H]〉 ∼ −0.6) with some contribution from the metal-rich component of the nearby halo. Here we report first results for 1799 stars. The distribution of radial velocity (RV) as a function of l for these stars shows (1) the expected thick disk population and (2) local metal-rich halo stars moving at high speeds relative to the disk, which in some cases form distinct sequences in RV–l space. High-resolution echelle spectra taken for 34 of these “RV outliers” reveal the following patterns across the [Ti/Fe]–[Fe/H] plane: 17 of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way, 8 have abundances coincident with those of the Galactic disk and a more metal-rich halo, and 9 of the stars fall on the locus defined by the majority of stars in the halo. The chemical abundance trends of the RV outliers suggest that this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas in situ on their current orbits. These results are consistent with scenarios where the stellar halo, at least as probed by M giants, arises from multiple formation mechanisms; however, when taken at face value, our results for metal-rich halo giants suggest a much higher proportion to be accreted than found by Carollo et al. and more like the fraction suggested in the analysis by Nissen & Schuster and Schuster et al. We conclude that M giants with large RVs can provide particularly fruitful samples to mine for accreted structures and that some of the velocity sequences may indeed correspond to real physical associations resulting from recent accretion events.
DOI：
10.1088/0004-637x/728/2/102
发表时间：
2010-12
期刊：
The Astrophysical Journal
影响因子：
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作者：
Mary E. K. Williams;M. Steinmetz;Sanjib Sharma;J. Bland-Hawthorn;R. D. Jong;G. Seabroke;A. Helmi;K. Freeman;J. Binney;I. Minchev;O. Bienaym'e;R. Campbell;J. Fulbright;B. Gibson;G. Gilmore;E. Grebel;U. Munari;J. Navarro;Q. Parker;W. Reid;A. Siebert;A. Siviero;F. Watson;R. Wyse;T. Zwitter
通讯作者：
Mary E. K. Williams;M. Steinmetz;Sanjib Sharma;J. Bland-Hawthorn;R. D. Jong;G. Seabroke;A. Helmi;K. Freeman;J. Binney;I. Minchev;O. Bienaym'e;R. Campbell;J. Fulbright;B. Gibson;G. Gilmore;E. Grebel;U. Munari;J. Navarro;Q. Parker;W. Reid;A. Siebert;A. Siviero;F. Watson;R. Wyse;T. Zwitter
DOI：
10.1086/588032
发表时间：
2007-05
期刊：
The Astrophysical Journal
影响因子：
--
作者：
E. Bell;D. Zucker;V. Belokurov;Sanjib Sharma;K. Johnston;J. Bullock;D. Hogg;K. Jahnke;J. D.
通讯作者：
E. Bell;D. Zucker;V. Belokurov;Sanjib Sharma;K. Johnston;J. Bullock;D. Hogg;K. Jahnke;J. D.