We combine the Siding Spring Survey of RR Lyrae stars with the Southern Proper Motion Catalog 4, in order to detect and kinematically characterize overdensities in the inner halo of the Milky Way. We identify one such overdensity above the Galactic plane, in quadrant 4 of the Galaxy. The overdensity extends at least 20 degrees in longitude, has an average heliocentric distance of 8 kpc with a depth of 4 kpc, and is confined within 4 kpc of the Galactic plane. Its metallicity distribution is distinct from that of the field population having a peak at -1.3 and a pronounced tail to -2.0. Proper motions indicate a net vertical motion away from the plane, and a low orbital angular momentum. Qualitatively, these orbit properties suggest a possible association with omega Centauri's parent satellite. However, comparison to a specific omega Cen N-body disruption model does not give a good match with observations. Line-of-sight velocities, and more extensive N-body modelling will help clarify the nature of this overdensity.
Signatures of a Tidally Induced Spiral Arm at the Anticenter of the Milky Way and a Kinematically Extended Anticenter Stream Using DESI DR2
University of California, Santa Cruz（加州大学圣克鲁兹分校）；University of Edinburgh（爱丁堡大学）；University of Toronto（多伦多大学）；University of Michigan（密歇根大学）；Observatório Nacional（国家天文台）；Shanghai Jiao Tong University（上海交通大学）
Tracing the very early disruption of the Sagittarius dwarf galaxy in the distant Milky Way halo
University of Groningen（格罗宁根大学）；University of Victoria（维多利亚大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森天体物理中心）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）
蛇夫座流是最近在银河系中发现的恒星潮汐流。我们提出了高质量的光谱数据的14个流成员星获得的凯克和MMT望远镜。我们确认流作为一个快速移动（$v_{los}\sim290$ km s $^{-1}$），运动学冷组（$σ_{v_{los}}\lesssim1$ km s $^{-1}$）的$α$增强和金属贫星（${\rm [α/Fe]\sim0.4}$ dex，${\rm [Fe/H]\sim-2.0}$ dex）。使用概率技术，我们同时在视线速度，颜色幅度，坐标和自行空间中对流进行建模，从而确定其在6D相空间中的分布。我们发现，这条流延伸到距离太阳7.5 ~ 9 kpc的地方;它的长度是宽度的50倍，只是在投影中看起来高度缩短。对这条星流中恒星的分析表明，它的年龄是$\sim12$ Gyr，其初始恒星质量是$\sim2\times10^4$ $M_{\odot}$（或至少是$\gtrsim7\times10^3$ $M_{\odot}$）。假设一个基准的银河系势，我们拟合一个与观测到的相空间分布相匹配的流轨道，除了在自行中的一些张力：流的轨道周期为$\sim350$ Myr，并且在一个相当偏心的轨道（$e\sim0.66$）上，近心为$\sim3.5$ kpc，远心为$\sim17$ kpc。该流的相空间结构和恒星数量表明，它的前身一定是一个球状星团，它在百万年前只被$\sim240…
A 3D Chemodynamical Census of Inner-Galaxy Metal-poor Giants to [Fe/H]~-3.5
Peking University（北京大学）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；University of Notre Dame（圣母大学）；Joint Institute for Nuclear Astrophysics – Center for the Evolution of the Elements (JINA-CEE)（核天体物理联合研究所——元素演化中心）；Shanghai Jiao Tong University（上海交通大学）
