明亮的QUEST RR天琴座恒星的光谱：朝向室女座的速度子结构
Spectroscopy of Bright QUEST RR Lyrae Stars: Velocity Substructures toward Virgo
摘要：
利用43颗明亮（V<16.1，距离<13 kpc）RR型天琴座星（RRLS）的光谱径向速度和金属丰度，我们发现室女座超密度（VOD）是由几个独立的晕子结构造成的。虽然在这些恒星的空间分布中几乎没有晕子结构的证据，但它们的径向速度分布揭示了两个移动的群体。当样本与SDSS中识别出的蓝色水平分支恒星样本结合时，这些结果得到了加强，并且合并后的样本为一个额外的移动群提供了证据。这些星群对应于SEGUE最近在同一方向观测到的F型主序星样本径向速度分布的峰值，尽管在一种情况下RRLS和F星群可能不在同一距离。其中一个新的子结构的金属丰度范围非常窄，这更符合它是来自被摧毁的球状星团的碎片，而不是来自矮星系。一小部分恒星的径向速度与先前在RRLS的一个较暗样本中发现的室女座恒星流（VSS）相似。我们的研究结果表明，这一功能延伸到距离短至12 kpc，从它以前的检测在~19 kpc。没有一个新的星系群，样本中只有一颗恒星的速度与人马座矮椭球星系的领先潮汐流一致，一些作者认为这是VOD的起源。
英文摘要：
Using a sample of 43 bright (V<16.1, distance <13 kpc) RR Lyrae stars (RRLS) from the QUEST survey with spectroscopic radial velocities and metallicities, we find that several separate halo substructures contribute to the Virgo overdensity (VOD). While there is little evidence for halo substructure in the spatial distribution of these stars, their distribution in radial velocity reveals two moving groups. These results are reinforced when the sample is combined with a sample of blue horizontal branch stars that were identified in the SDSS, and the combined sample provides evidence for one additional moving group. These groups correspond to peaks in the radial velocity distribution of a sample of F type main-sequence stars that was recently observed in the same directon by SEGUE, although in one case the RRLS and F star groups may not lie at the same distance. One of the new substructures has a very narrow range in metallicity, which is more consistent with it being the debris from a destroyed globular cluster than from a dwarf galaxy. A small concentration of stars have radial velocities that are similar to the Virgo Stellar Stream (VSS) that was identified previously in a fainter sample of RRLS. Our results suggest that this feature extends to distances as short as ~12 kpc from its previous detection at ~19 kpc. None of the new groups and only one star in the sample have velocities that are consistent with membership in the leading tidal stream from the Sagittarius Dwarf Spheroidal Galaxy, which some authors have suggested is the origin of the VOD.
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