基于LAMOST和GAIA的Magellanic Stream化学-动力学研究

Exploring the interactions between the Milky Way and its neighbor dwarf galaxies, such as Large/Small Magellanic Clouds, could help us better understanding the models of the Galactic gravitational potential and distributions of total matters including baryonic and dark matters. Furthermore, such studies could provide better constrains on present Universal and galactic evolution model and simulations. In this program, we intend to study the formation and evolution of the Leading Arm (LA) of the Magellanic Stream (MS) by using kinematic data from GAIA and abundance information from LAMOST. Comparing the information statistically with the ones of Milky Way and its neighbor dwarf galaxies, we could understand the sources of the LA matter and could solve contradicts between present simulations and observation. Moreover, with calculations and statistics of ages for the large LA member sample, it is possible for us to test present hypothesis about the formation of the LA multi-branch morphology. Besides, it is first time that we will calculate and analysis distances of the LA members, in order to explore the space distribution of the LA and better understand the models of the Galactic gravitational potential and distributions of its total matters. In conclusion, this program will present some significant results in this region via combing and using data from LAMOST and GAIA.

通过研究银河系与邻近矮星系之间的相互作用，不但可以帮助我们了解银河系及其邻近矮星系的总物质质量分布情况，更为重要的是可以勾勒出近邻宇宙暗物质质量的分布图景，从而对现今的星系宇宙学模型提供进一步的物理约束、并对相关理论及数值模拟加以完善。本项目计划利用GAIA的全天测量数据获取目前最大样本、位于银河系盘附近、隶属Magellanic Stream（MS）Leading Arm（LA）部分的年轻恒星的空间运动学多维参数，结合LAMOST巡天获取的海量恒星光谱数据，首次对LA成员星的金属元素丰度和运动学信息进行统计分析，探究LA的物质起源、解决目前相关理论模型与观测结果之间的矛盾；推测LA中恒星诞生的可能性和概率，验证LA结构的形成假说；确定LA形成的空间位置和分布，加深对MW引力势和物质分布模型的了解。该项目通过LAMOST与GAIA的充分结合，将在相关领域获得具有较高显示度的重要成果。

本项目的主要研究内容有：1）搜寻并证认位于银盘的Magellanic Stream（MS）中Leading Arm（LA）的成员星；2）系统研究LA成员星的金属元素丰度以及运动学；3）系统研究LA的起源。我们用智利的MIKE@Magellan望远镜对位于LA的15颗样本星拍摄了高分辨光谱，并对原始数据进行了平场改正、波长定标、一维谱抽取以及流量改正。我们开发了一个可视化的GUI软件，结合TLUSTY大气模型和SYNSPEC光谱综合程序，通过对观察侧光谱的拟合来确定样本星的大气参数和多种元素丰度。结合Gaia DR2的自行数据，我们计算了样本星在银河系坐标下的三维速度、角动量，以及在银河系引力势下的轨道和势能，并将这些结果与丰度结果一起和银河系盘上的O/B型星的结果相比较，从中找出了四颗可能属于LA部分，且年龄小于LA演化时标的恒星。通过样本星的化学-运动学信息，我们推测LA的物质更有可能起源于大麦哲伦云，而非之前理论模拟研究中所假设的小麦哲伦云；此外LA中有恒星诞生这一观测证据间接验证了假说——LA是MS与银河系的重子物质盘和球状的暗物质晕（或是一单独的暗物质盘）再次发生相互作用后的产物。该项目共发表SCI论文15篇，会议论文1篇。