标题： 金属贫乏场中的两种RR Lyrae星群 显示英文标题

标题： Two populations among the metal-poor field RR Lyrae stars

摘要： 我们利用文献中提供的自行速度、视向速度和光测距离，计算了209颗金属贫乏的$([Fe/H] < -1.0)$RR Lyrae (ab)变星在太阳邻域的空间速度分量和银河系轨道要素。 我们观察到当相对于局部静止标准的特殊速度超过阈值值$V_{\rm pec}\approx 280$\mbox{km s$^{-1}$}时，恒星的空间和运动学特征出现突然变化。 这提供了证据，表明金属贫乏的RR Lyrae恒星的总体不是均匀的，而是包括两个占据银河系不同体积的球形子系统。 基于场RR Lyrae恒星相应子系统的典型参数与我们之前研究的球状星团之间的吻合，我们得出结论，金属贫乏恒星和球状星团可以分为两个群体，但使用不同的标准来区分恒星和星团。 我们认为，具有快速运动的场恒星和具有更红水平分支的星团构成了吸积外晕的球状子系统，其大小大约是第一个子系统的两倍。 它完全没有金属丰度梯度，其大部分恒星具有高偏心率轨道，许多恒星在银河系中表现出逆行运动，它们的年龄相对较低，支持该子系统中的天体具有河外起源的假说。 显示英文摘要

摘要： We compute the spatial velocity components and the galactic orbital elements for 209 metal-poor $([Fe/H] < -1.0)$ RRLyrae (ab) variable stars in the solar neighborhood using proper motions, radial velocities, and photometric distances available in the literature. We observe abrupt changes in the stellar spatial and kinematical characteristics when the peculiar velocities relative to the local standard of rest cross the threshold value, $V_{\rm pec}\approx 280$ \mbox{km s$^{-1}$}. This provides evidence that the general population of metal-poor RRLyrae stars is not uniform, and includes two spherical subsystems occupying different volumes in the Galaxy. Based on the agreement between typical parameters of corresponding subsystems of field RRLyrae stars and of the globular clusters, studied by us earlier, we conclude that metal-poor stars and globular clusters can be subdivided into two populations, but using different criteria for stars and clusters. We suppose that field stars with fast motion and clusters with redder horizontal branches constitute the spheroidal subsystem of the accreted outer halo, with is approximately two times larger in size than the first subsystem. It has absolutely no metallicity gradients, most of its stars have eccentric orbits, many stars display retrograde motion in the Galaxy, and their ages are comparatively low, supporting the hypothesis that the objects in this subsystem have an extragalactic origin.