UVES detailed chemical abundances in the Sgr dSph and the CMa overdensity

In this contribution, we present detailed chemical abundances on two stellar systems presently believed to be undergoing tidal merging with the Milky Way (MW). The first one is the Sagittarius Dwarf Spheroidal (Sgr dSph, [5]), a massive (10 M⊙) dSph orbiting along a very short period (< 1GY r) almost polar orbit inside the Halo, along which is slowly dissolving in a huge stellar stream [6]. The second object is the recently discovered, and still controversial CMa dwarf galaxy [8], a heavily degraded overdensity embedded in the MW thick disk, believed to be the residual of an in-plane accretion of an object of mass comparable to the Sgr dSph. This interpretation is still controversial, since [9] claimed that the structure almost disappears, when disk warping and/or flaring is properly taken into account in the modeling of the MW contribution.