论文标题
摆的挥杆:局部恒星光环的化学动力学表明了几个径向合并事件的贡献
A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
论文作者
论文摘要
我们发现,局部恒星光环中的峰值和galah恒星的化学丰度和动力学与一种情况不一致,在这种情况下,内部光环主要由单个,大规模的古代合并事件中的碎屑组成,正如提出的那样解释了Gaia-enceladus/gaia sausage(GSE)结构。数据包含具有能量的化学成分趋势,与对单个大规模的古代合并事件的期望相反,并且存在具有不同动力学的多个化学演化路径。我们使用贝叶斯高斯混合物模型回归算法来表征局部恒星光环,并发现数据最适合具有四个组件的模型。我们将这些组件解释为VRM,Cronus,Nereus和Thamnos。但是,由于其成员恒星的化学丰度分布包含许多峰,因此Nereus和Thamnos可能代表多个积聚事件。尽管Cronus和Thamnos组件具有不同的动力学,但它们的化学丰度表明它们可能是相关的。我们表明,Nissen&Schuster(2010)的独特低和高α光环种群由VRM和Cronus Stars以及一些原位恒星解释。由于局部恒星光环包含多个子结构,因此选择GSE恒星的不同流行方法实际上会选择这些子结构的不同混合物,这可能会改变所选恒星的明显化学动力学特性。我们还发现,太阳能区域中的飞溅恒星转移到V_PHI更高,而[Fe/H]略低于先前报道的。
We find that the chemical abundances and dynamics of APOGEE and GALAH stars in the local stellar halo are inconsistent with a scenario in which the inner halo is primarily composed of debris from a single, massive, ancient merger event, as has been proposed to explain the Gaia-Enceladus/Gaia Sausage (GSE) structure. The data contains trends of chemical composition with energy which are opposite to expectations for a single massive, ancient merger event, and multiple chemical evolution paths with distinct dynamics are present. We use a Bayesian Gaussian mixture model regression algorithm to characterize the local stellar halo, and find that the data is best fit by a model with four components. We interpret these components as the VRM, Cronus, Nereus, and Thamnos; however, Nereus and Thamnos likely represent more than one accretion event because the chemical abundance distributions of their member stars contain many peaks. Although the Cronus and Thamnos components have different dynamics, their chemical abundances suggest they may be related. We show that the distinct low and high alpha halo populations from Nissen & Schuster (2010) are explained by VRM and Cronus stars, as well as some in-situ stars. Because the local stellar halo contains multiple substructures, different popular methods of selecting GSE stars will actually select different mixtures of these substructures, which may change the apparent chemodynamic properties of the selected stars. We also find that the Splash stars in the solar region are shifted to higher v_phi and slightly lower [Fe/H] than previously reported.