First results of UVES at VLT: abundances in the Sgr dSph

Two giants of the Sagittarius dwarf spheroidal have been observed with the UVES spectrograph on the ESO 8.2m Kueyen telescope, during the commissionin g of the instrument. Sgr 139 has [Fe/H] = -0.28 and Sgr 143 [Fe/H]= -0.21, these values are considerably higher than photometric estimates of the meta llicity of the main population of Sgr. We derived abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y, Ba, La, Ce, Nd and Eu; the a bundance ratios found are essentially solar with a few exceptions: Na shows a strong over-deficiency, the heavy elements Ba to Eu, are overabundant, w hile Y is underabundant. The high metallicity derived implies that the Sgr galaxy has experienced a high level of chemical processing. The stars had b een selected to be representative of the two main stellar populations of Sa gittarius, however, contrary to what expected from the photometry, the two stars show a very similar chemical composition. We argue that the most like ly explanation for the difference in the photometry of the two stars is a d ifferent distance, Sgr 143 being about 2 Kpc nearer than Sgr 139. This resu lt suggests that the interpretation of colour - magnitude diagrams of Sgr i s more complex than previously thought and the effect of the line of Sight depth should not be neglected. It also shows that spectroscopic abundances are required for a correct interpretation of Sgr populations.