Measurement of Halo Substructure by RR Lyrae Star Surveys

津恩博士和他的团队研究银河系晕的吸积历史。这项工作测试的吸积范式和双晕图片。如果光环是在数十亿年的时间里通过许多矮卫星星系的吸积和潮汐破裂而形成的，那么它将包含来自破裂星系的恒星流，这些恒星流可以作为恒星密度增强的区域（光环子结构）和在太空中一起移动的恒星来检测。外晕可能主要由潮汐摧毁的卫星星系的恒星组成，而内晕可能起源于吸积气体或最初合并形成银河系的物体。据认为，晕有两个主要组成部分，不同的恒星运动学，空间分布和金属丰度分布。然而，只有一小部分的晕已经调查，和一些已知的晕子结构的属性是很差的确定。晕中不同的子结构和流可以追溯到天琴座RR型星。这些脉动星很容易通过它们的半天周期和大约一等的振幅来识别。这项研究将提供以前检测到的晕子结构的更好的距离和大小，并在尚未调查的天空区域寻找新的子结构。这项工作使用了在LaSilla-QUEST调查中发现的距离太阳约60 kpc的天琴座RR星。光谱观测被用来确定是否可疑的子结构是真实的群体的共同运动的恒星，预计剩余的吸积卫星星系。径向速度和金属丰度的测量约150 RR天琴座星的内晕，以测试是否RR天琴座星分为两个组件，或相反，集中在吸积晕。本计画训练研究生与本科生光学光度学与光谱学的技术。作为推广活动的一部分，将为耶鲁大学莱特纳家庭天文台和天文馆制作一个关于银河系演化的节目。

Dr. Zinn and his team study the accretion history of the halo of the Milky Way galaxy. This work tests the accretion paradigm and the dual halo picture. If the halo was built up over billions of years through the accretion and tidal disruption of many dwarf satellite galaxies, it will contain streams of stars from disrupted galaxies that are detectable as regions of enhanced stellar density (halo substructures) and as stars moving together through space. The outer halo may consist primarily of stars from tidally destroyed satellite galaxies, whereas the inner halo may have originated in situ from accreted gas or within the very first objects that merged to form the Galaxy. It is recognized that the halo has two major components that differ in stellar kinematics, spatial distribution, and metallicity distribution. However only a small fraction of the halo has been surveyed, and properties of some known halo substructures are poorly determined. The different sub-structures and streams in the halo are traceable with RR Lyrae stars. These pulsating stars are easily recognized by their half-day periods and about one magnitude amplitudes. This research will provide better distances and sizes of previously detected halo substructures and look for new substructures in yet to be surveyed areas of the sky. This work uses RR Lyrae stars found in the LaSilla-QUEST survey up to about 60 kpc from the Sun. Spectroscopic observations are used to identify if suspected substructures are real groups of co-moving stars, as expected for remains of accreted satellite galaxies. Radial velocities and metallicities are measured for about 150 RR Lyrae stars in the inner halo to test whether RR Lyrae stars separate into two components, or are instead concentrated in the accreted halo. This project trains graduate and undergraduate students in the techniques of optical photometry and spectroscopy. As part of the outreach activities, a show on the evolution of the Milky Way galaxy will be created for Yale's Leitner Family Observatory and Planetarium.