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

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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.