Two giants of the Sagittarius dwarf spheroidal have been observed with the UVES spectrograph on the ESO 8.2m Kueyen telescope , during the commissioning 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 metallicity 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 abundance ratios found are essentially solar with a few exceptions : Na shows a strong overdeficiency , the heavy elements Ba to Eu , are overabundant , while Y is underabundat .
The high metallicity derived implies that the Sgr galaxy has experienced a high level of chemical processing .
The stars had been selected to be representative of the two main stellar populations of Sagittarius , however , contrary to what expected from the photometry , the two stars show a very similar chemical composition .
We argue that the most likely explanation for the difference in the photometry of the two stars is a different distance , Sgr 143 being about 2Kpc nearer than Sgr 139 .
This result suggests that the interpretation of colour – magnitude diagrams of Sgr is 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 .