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We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi)dwarf spheroidal (dSph) galaxies based on published and new Keck HIRES spectrafor stars in the outer UMi field. Washington+DDO51 filter photometric catalogsprovide additional leverage on membership of individual stars, and beyond 0.5King limiting radii (R_lim) identify bona fide dSph members up to 4.5 timesmore efficiently than simple color-magnitude diagram selections. Previouslyreported ``cold populations'' R_lim are not obvious in the data and appear onlywith particular binning; more or less constant and platykurtic dispersionprofiles are characteristic of these dSphs to large radii. We report discoveryof UMi stars to at least 2.7 R_lim (i.e.,210 arcmin or 4 kpc). Even withconservative assumptions, a UMi mass of M > 4.9 x 10^8 M_(sun) is required tobind these stars, implying an unlikely global mass-to-light ratio of M/L > 900(M/L)_(sun). We conclude that we have found stars tidally stripped from UMi.Comment: 9 pages, 4 figures. Published in the Astrophysical Journal Letter

astrophysical journal/the astrophysical journal

Exploring Halo Substructure with Giant Stars: The Velocity Dispersion Profiles of the Ursa Minor and Draco Dwarf Spheroidal Galaxies at Large Angular Separations