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  • MAGELLAN/M2FS SPECTROSCOPY ...
    Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; III, John I. Bailey; Koposov, Sergey E.; Belokurov, Vasily; Evans, N. Wyn

    The Astrophysical journal, 07/2015, Volume: 808, Issue: 2
    Journal Article

    ABSTRACT We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity ( , median random error km s−1), effective temperature ( , K), surface gravity ( , dex), and iron abundance ( , dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of km s−1 about a mean of km s−1 in the solar rest frame ( km s−1 in the Galactic rest frame), and a metallicity dispersion of dex about a mean of . These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars-both of which must be checked with deeper imaging and repeat spectroscopic observations-the estimated velocity dispersion suggests a dynamical mass of enclosed within projected halflight radius pc, with mass-to-light ratio in solar units.