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Paper: Stellar Kinematics and Metallicities in the Draco and Ursa Minor Dwarf Spheroidal Galaxies from WHT/AF2-WYFFOS
Volume: 507, Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys, and Wide Fields
Page: 241
Authors: Jin, S.; Irwin, M.; Tolstoy, E.; Lewis, J.; Hartke, J.
Abstract: We present preliminary results from our chemo-dynamical survey of two Milky Way dwarf spheroidal (dSph) galaxies, Draco and Ursa Minor. The two galaxies have similar radial velocities and reside in close proximity in the outskirts of the Milky Way halo, yet exhibit noteworthy differences in their morphologies. We obtained spectroscopic data with AF2-WYFFOS on the WHT for several hundred red-giant-branch (RGB) candidates in each galaxy out to its tidal radius, from which we have identified approximately 100 velocity members in each system. Metallicities are determined for the individual RGB stars using the Ca II triplet lines. Whereas Ursa Minor shows an RGB population of well-mixed metallicities, a clear gradient is observed in Draco, in which the outer regions host stars of lower [Fe/H]. Such differences may be a reflection of their differing morphologies, with Ursa Minor having been tidally stirred to give rise to both its highly elongated shape and a more mixed [Fe/H] distribution.
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