Program: GS-2006B-C-10

Though it is now clear that accretion of dwarf galaxies likely played a prominent role in creating the Milky Way (MW) halo, the chemical abundance patterns of current MW satellites are typically very different than those of halo stars, and the reason for these differences remains a matter of speculation. We propose to test the bridge from dwarf galaxy to halo star {\it directly} by exploring chemical trends along the tidal tails of disrupting dwarf galaxies. Our initial abundance analysis on debris from the Sagittarius (Sgr) dwarf galaxy has already revealed a significant [Fe/H] trend along the leading arm from the core to debris stripped some 2 Gyr ago from the satellite. This trend vividly demonstrates the origin of differences between current dwarf galaxies and the stars they contributed to the halo and presents a new method for mapping the star formation and dynamical histories of galaxies. We propose to improve our analysis of the Sgr stream by undertaking echelle resolution observations of stars in the dynamically simpler {\it trailing arm} of Sgr. We also plan to repeat this analysis on the Monoceros (Mon)/Canis Major/Argo and Tri-And systems to: (1) establish whether Mon is a satellite tidal stream and not the Galactic warp, (2) test the putative associations of Canis Major, Argo and Tri-And with Mon, and (3) search for abundance variations along the Mon stream like those seen for the Sgr stream.