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

Abstract

We present detailed Chemical abundances for 12 stars in the Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph) and 3 in the Canis Mayor Overdensity (CMa), based on UVES spectra. Sgr dSph stars present high metallicity ([Fe/H] between -1 and 0) low [alpha/Fe] ratios, overabundant La, Ce and Nd, underabundant Na, Al,Ni and Zn. Zn underabundance in particular is interesting, since it may undermine the parallel drawn between dSph and DLAs, where Zn is used as a proxy for Fe. Of the three CMa stars, one is likely a Milky Way (MW) interloper, the other two present solar metallicity, underabundant alpha elements and overabundant La, Ce and Nd. These features are strongly resembling what found in Sgr dSph. Moreover, a significant Cu overabundance is detected ([Cu/Fe] ~ +0.25), unusual for MW disk stars. In our opinion these results strongly point toward the presence, in the CMa overdensity, of an accreted stellar population of extragalactic origin.