Fossils of Reionization: The Search for the Most Metal-Poor Stars in the Local Group

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Dr. Simon and his team undertake a search of the Milky Way's four southern dwarf spheroidal satellites to identify and characterize extremely metal-poor stars. Many of the dwarf galaxies orbiting the Milky Way host stars formed in the early universe. The elemental composition of these presumably ancient stars is very metal-poor (relative to their hydrogen content and elemental abundances in our sun). The chemical makeup of these stars holds clues how the earliest stars and the proto-galaxies formed. Existing surveys of the Milky Way halo have largely been mined but yielded only six stars with an iron abundance less than 1/10000 that of the Sun. It is known that nearby dwarf galaxies contain more extremely metal-poor stars than the galactic halo, and therefore these are ideal targets to search for and to learn more about extremely metal-poor stars. Highly efficient observations of about 6000 stars in these galaxies are planned using the Inamori Magellan Areal Camera and Spectrograph (IMACS) wide-field imager and multi-object spectrograph at the Magellan telescope, comprising a nearly complete, magnitude-limited sample. The Ca K line is used as a metallicity indicator to identify the most metal-poor objects. These stars are then observed at high spectral resolution to obtain new constraints on the elemental yields of the first supernovae, the initial mass function of the first stars, the nucleosynthesis sites responsible of producing of the heaviest elements, and the formation of the stellar halo of the Milky Way.Dr. Simon is partnering with Los Angeles-area teachers through the national outreach program Project ASTRO, which is run by the Astronomical Society of the Pacific. The program matches elementary through high school teachers with professional and amateur astronomers to bring astronomy into their classrooms. Dr. Simon's new Project ASTRO activity is directly related to the current research on the production of chemical elements in stars through cosmic time, and their dispersal by supernova explosions that allows them to be incorporated into new stars, planets, and life.