PI: Allyson A. Sheffield, Vassar College, firstname.lastname@example.org
Address: Physics Department, 124 Raymond Ave., Box 0052, Poughkeepsie, NY 12604-0052, USA
CoI: Steven R. Majewski, University of Virginia
Title: Exploring the Chemical Nature and Origin of Potential Galactic Substructures
Abstract: Hierarchical formation models predict that galaxies form over time via the buildup of subgalactic fragments. Relics of past accretion events are manifested as substructures in a galaxy. Coherent streams of stars from accreted Milky Way dwarf spheroidals have indeed been detected wrapping around the Milky Way, as well as other nearby galaxies, lending strong support to the hierarchical formation paradigm. Stars from accreted dwarf spheroidals have undergone a different enrichment history than Milky Way field stars and, thus, can be ``chemically tagged''. In particular, Milky Way dwarf spheroidal stars have lower [(alpha)/Fe] values than Milky Way field stars at the same [Fe/H]. In a medium-resolution survey of late-type giants in the Galactic thick disk and nearby halo, we identified several groups of stars that show coherence in their radial velocities and have lower Mg/Fe values as a function of [Fe/H] than the bulk of the thick disk stars in the survey. These trends are suggestive of substructures. We propose to obtain high-resolution echelle spectroscopy of stars in these groups. Our goal is to determine the precise chemical abundances of stars in these putative substructures, allowing us to probe their nature and further understand the accretion history of the Milky Way.
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