Learning how the Milky Way was Assembled through Measurements of Positions, Velocities and Elements in Stars in the Halo

银河系是我们在宇宙中的家。 银河系是我们了解周围宇宙中数千亿个星系的最重要参考。它是唯一一个我们可以详细观察单个恒星的星系，比如我们的太阳。然而，关于银河系和我们今天看到的结构，仍然有一些基本的问题没有得到解答。我们仍然不知道银河系的质量在两倍之内。关于星系如何形成，最被接受的模型是星系通过与较小的卫星星系合并而成长。 研究人员将通过对银河系外部古老恒星的光学观测来检查这个模型，称为Halo。利用光谱，研究人员将测量这些恒星中元素的丰度，这可以告诉我们这些古老恒星诞生的原始较小星系。当与这些恒星的其他观测相结合时，研究人员将能够回答有关我们银河系历史的基本问题。星系晕中恒星的深层光谱学为这些恒星的自行运动增加了视线速度，化学丰度信息和改进的距离估计。 研究人员的观测将确定速度的三个分量，每个星星在银河系中位置的三个分量，以及星星的临界第七维元素丰度。光谱和自行将被测量的主序星距离为90千秒差距。总的来说，这个程序将获得450个主序晕星在晕中11个不同视线的光谱。这些数据包含有关银河系恒星晕生长和卫星吸积的独特信息，这些信息将用于重建银河系的质量吸积历史。此外，完整的相空间信息将用于测量银河系的总质量;这是一个重要的，但约束条件很差的天体物理量。来自研究者自行数据的横向速度信息将用于测量遥远晕星的速度各向异性。速度各向异性是我们对银河系总质量的认识中系统不确定性的一个主要来源。研究人员将从多维数据中寻找遥远晕中的子结构，特别是来自低光度卫星的子结构。这些矮星系的潮汐遗迹在以前的搜索中被隐藏起来。测量低光度晕祖细胞的数量将测试暗物质次晕和矮卫星星系之间的联系模型。这是对宇宙学星系形成模型预测的一个重要的一致性检验。从三维速度，研究人员将测量被吸积到光环中的祖先系统的轨道。从金属丰度，可以估计的祖先的光度。将测量样本中较亮恒星的α元素丰度，并用于估计卫星的吸积时间。星系晕的轨道、吸积时间和光度的分布决定了星系晕的吸积历史。他们的推广计划包括通过加州大学圣克鲁斯科学实习计划（SIP）引进高中生。 高中SIP实习生与他们的导师一起从事研究项目，过去的实习生在天文学会会议上发表论文，并成为被评审出版物的合著者。两名研究生将与研究人员合作指导学生。 这将使研究生在非课堂教学的经验。研究生将为高中生开发一个基于Python的研究方法模块，该模块借鉴了研究计划。调查人员将通过参与SIP，研究方法，加州数学和科学暑期学校以及圣克鲁斯县监狱的囚犯教育项目等项目，努力增加代表性不足的少数民族在STEM领域的参与。

The Milky Way Galaxy is our home in the universe. The Milky Way is our most important reference for understanding the hundreds of billions of galaxies in the universe around us. It is the only galaxy where we can observe individual stars, like our sun, in detail. However, there remain fundamental unanswered questions about the Milky Way and the structure we see today. We still do not know the mass of our Galaxy to within a factor of two. The most accepted model for how galaxies form is that galaxies grow by merging with smaller satellite galaxies. The investigators will check this model by optical observations of ancient stars in the outer parts of the Milky Way, called the Halo. Using optical spectra, the investigators will measure the abundance of elements in these stars, which can tell us about the original, smaller, galaxies in which those old stars were born. When combined with other observations of these stars, the investigators will be able to answer basic questions about the history of our own Milky Way galaxy.The deep spectroscopy of stars in the galactic halo add line-of-sight velocity, chemical abundance information and improved distance estimates to the proper motions for these stars. The investigators' observations will determine the three components of the velocity, three components of each star's position in the Galaxy and a critical seventh dimension elemental abundances of the star. The spectroscopy and proper motions will be measured for main sequence stars as distant as 90 kpc. In total, this program will obtain spectra for 450 main sequence halo stars over 11 different lines of sight in the halo. These data contain unique information about the growth of the Milky Way's stellar halo and accretion of satellites, which will be used to reconstruct the mass accretion history of our Galaxy. Furthermore, the full phase-space information will be used to measure the total mass of the Milky Way; an important, yet poorly constrained, astrophysical quantity. The transverse velocity information from the investigator's proper motion data will be used to measure the velocity anisotropy of distant halo stars. The velocity anisotropy is a major source of systematic uncertainty in our knowledge of the total mass of the Milky Way. The investigators will search the multi-dimensional data for substructure in the distant halo, especially substructure from low luminosity satellites. The tidal remnants of these dwarf galaxies have been hidden from previous searches. Measuring the number of low-luminosity halo progenitors will test models for the connection between dark matter sub-halos and dwarf satellite galaxies. This is an important consistency test of the predictions of cosmological galaxy formation models. From the three dimensions of velocity, the investigators will measure the orbits of the progenitor systems that were accreted into the halo. From the metallicities, the luminosities of the progenitors can be estimated. The abundances of the alpha-elements will be measured for the brighter stars in the sample and used to estimate the accretion times of the satellites. The distributions of orbits, accretion times and luminosities of the progenitors defines the accretion history of our Galaxy's halo. Their outreach plan includes bringing in high school students via the UC Santa Cruz Science Internship Program (SIP). High school SIP interns work with their mentors on research projects, and past interns have presented papers at Astronomical Society meetings and have been co-authors on refereed publications. The two graduate students will mentor the students in collaboration with the investigators. This will give the graduate students experience in non-classroom teaching. Graduate students will develop a Python-based research methods module for high school students that draws from the research program. The investigators will work to increase the participation of underrepresented minorities in STEM fields through their participation in programs like SIP, Research Methods, the California State Summer School for Mathematics and Science and the Project for Inmate Education in the Santa Cruz county jail.