Kapteyn选定区域103的自行：室女座恒星流的初步轨道
Proper Motions in Kapteyn Selected Area 103: A Preliminary Orbit for the Virgo Stellar Stream
摘要：
本文给出了Kapteyn选定区域（SA）103中的绝对自行。该区域位于室女座恒星流中心以西7度（VSS，Duffau等人，2006），具有代表该恒星流的明确的主层序。在SA 103中，我们根据它的金属丰度、径向速度和距离将一颗RR型天琴座星确定为VSS的成员。VSS候选关闭星和次巨星的自行与天琴座RR星一致。三维速度数据表明，轨道的近心点为11千秒差距，远心点约为90千秒差距。因此，VSS包括在高度破坏性轨道近心附近发现的潮汐碎片。通过对距离银河系中心大于50千秒差距的6个球状星团和VSS的轨道进行研究，我们发现了一个暂定的星协，NGC 2419。我们推测NGC 2419可能是一个破裂系统的核心，VSS是其中的一部分。
英文摘要：
We present absolute proper motions in Kapteyn Selected Area (SA) 103. This field is located 7 degrees west of the center of the Virgo Stellar Stream (VSS, Duffau et al. 2006), and has a well-defined main sequence representing the stream. In SA 103 we identify one RR Lyrae star as a member of the VSS according to its metallicity, radial velocity and distance. VSS candidate turnoff stars and subgiant stars have proper motions consistent with that of the RR Lyrae star. The 3D velocity data imply an orbit with a pericenter of 11 kpc and an apocenter of ~90 kpc. Thus, the VSS comprises tidal debris found near the pericenter of a highly destructive orbit. Examining the six globular clusters at distances larger than 50 kpc from the Galactic center, and the proposed orbit of the VSS, we find one tentative association, NGC 2419. We speculate that NGC 2419 is possibly the nucleus of a disrupted system of which the VSS is a part.
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