Collaborative Research: Towards the Edge of the Milky Way. The First Contiguous Spectroscopic Survey of the True Outer Halo.

我们恒星晕的长动力学时间和径向范围保留了一个机会来追踪我们银河系的恒星和暗物质成分的质量聚集的历史。我们对外晕的大部分了解都是从碰巧从附近经过的恒星那里学到的。如果外晕像我们预期的那样是动态年轻的，而且不是很好地混合，那么这些恒星的运动可能并不能完整地讲述银河系最近的吸积史。作为重子振荡光谱调查(BOSS)的一部分，Rockosi博士(加州大学圣克鲁斯分校)和莫里森博士(凯斯西储大学)正在对外晕中的红巨星分支恒星进行光谱测量。这是斯隆数字巡天(SDSS)-III项目中的黑暗时间调查。BOSS光谱仪的改进和对大约10,000平方度区域的大范围覆盖使我们能够对我们银河系的外部进行连续观测。完整的样本将提供大约1000颗恒星的运动学、金属度和阿尔法元素与铁的丰度比，中值距离为50kpc，提供真正的外晕样本。氧、镁和硅等阿尔法元素主要产生于超新星中，并追踪着晕的化学演化。外晕样本将用于测量从银河系中心到100kpc以上的晕恒星径向密度分布、金属丰度和阿尔法元素丰度梯度，以及识别和表征恒星密度、运动学和化学丰度的亚结构。由此，我们可以了解恒星吸积对外晕的贡献，以及晕前体的质量、轨道分布和恒星形成历史。将外晕的这些测量值与现存的矮球星系和内晕的测量值进行比较，可以推断我们的银河系及其前身的质量增长历史和恒星群随时间的演化。SDSS的所有数据都及时公开，为天文学家提供了丰富的、在许多方面仍未开发的资源。主要研究人员在SDSS项目中领导了从提案到数据发布的出色调查。在过去的六年里，所有人都积极参与了在这些数据能够可靠地用于恒星之前所需的校准，包括改进SDSS光谱的通量校准，到对恒星参数的测试，以及对经过充分研究的疏散星团和球状星团的艰苦观察和分析。少数学生仍然是毕业博士的一小部分。凯斯天文学正在与非常成功的菲斯克/范德比尔特少数民族硕士桥项目合作，这样他们的毕业生就可以像目前进入范德比尔特博士项目一样进入凯斯西储大学天文学博士项目；有效地作为三年级研究生。女性在科学和工程领域的案例计划(由PI共同创立)目前已进入第九个年头，鼓励女性本科生留在科学领域。Rockosi博士领导了许多项目，以开发Keck和Lick天文台的设备仪器。这些仪器可通过公开访问Keck获得，而Lick天文台项目为自适应光学和其他仪器研究提供了一个技术开发平台。洛科西博士和她的研究小组参与了圣克鲁斯科学与工程教育者研究所，该研究所向研究生和博士后介绍基于探究的学习技术，同时举办研讨会，鼓励代表人数较少的少数族裔学生继续攻读STEM领域的高级学位。该项目约75%的本科生参与者是女性或代表性不足的少数族裔。

The long dynamical times and radial extent of our stellar halo preserves a chance to trace the history of mass assembly of both the stellar and dark matter components of our Galaxy. Most of what we know about the outer halo is learned from stars that happen to pass nearby. If the outer halo is, as we expect, dynamically young and not well mixed, the motion of such stars may not tell the full story of the recent accretion history of the Galaxy. Dr. Rockosi (at the University of California Santa Cruz) and Dr. Morrison (at Case Western Reserve University)work on a spectroscopic survey of red giant branch stars in the outer halo, done as part of the Baryon Oscillation Spectroscopic Survey (BOSS). This is the dark time survey in the Sloan Digital Sky Survey (SDSS)-III project. The BOSS spectrograph improvements and large area coverage of an area of about 10,000 square degrees allow a contiguous survey of the outer reaches of our Galaxy. The complete sample will provide kinematics, metallicities, and alpha element to iron abundance ratios for approximately 1000 stars with a median distance of 50 kpc, providing a true outer halo sample. The alpha elements such as O, Mg, and Si are mainly produced in supernovae and trace the chemical evolution of the halo. The outer halo sample will be used to measure the halo stellar radial density profile, metallicity and alpha element abundance gradients to beyond 100 kpc from the center of the Galaxy, as well as identify and characterize substructure in stellar density, kinematics and chemical abundance. From this we can learn the fractional contribution of stellar accretion to the outer halo, as well as the mass and orbit distributions and star formation histories of the halo progenitors. Comparison of these measurements in the outer halo to existing measurements in the surviving dwarf spheroidal galaxies and in the inner halo can be used to infer the mass accretion history and stellar population evolution of our Galaxy and its progenitors through time. All SDSS data become public in a timely manner, giving a rich and in many ways still unexplored resource to astronomers. The principal investigators have led the stellar surveys in the SDSS projects from proposals through data releases. All have been actively involved for the past six years in the calibrations needed before these data can be used reliably for stars, which included improving the flux calibration of the SDSS spectra, to tests of the stellar parameters pipeline to the painstaking observation and analysis of well-studied open and globular clusters.Minority students remain a small proportion of graduating PhDs. Case astronomy is partnering with the very successful Fisk/Vanderbilt Masters Bridge Program for minorities so that their graduates can enter the Case Western Reserve University astronomy PhD program in the same way that they currently enter the Vanderbilt PhD program; effectively as third-year graduate students. The Case program for Women in Science and Engineering (co-founded by the PI) is now in its ninth year of encouraging women undergraduates to stay in science. Dr. Rockosi leads many projects to develop facility instrumentation at Keck and Lick Observatory. These instruments are available via public access to Keck, and the Lick Observatory projects provide a technology development platform for adaptive optics and other instrumentation research. Dr. Rockosi and her research group participate in the Santa Cruz Institute for Science and Engineering Educators, which introduces graduate students and postdocs to inquiry-based learning techniques while running workshops designed to encourage underrepresented minority students to go on for advanced degrees in STEM fields. Approximately 75% of the undergraduate participants in this program are women or under-represented minorities.