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Astron. Astrophys. 359, 663-668 (2000)

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

P. Bonifacio 1, V. Hill 2, P. Molaro 1, L. Pasquini 2, P. Di Marcantonio 1 and P. Santin 1

1 Osservatorio Astronomico di Trieste, Via G.B.Tiepolo 11, 34131 Trieste, Italy
2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

Received 6 March 2000 / Accepted 4 May 2000

Abstract

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][FORMULA] and Sgr 143 [Fe/H][FORMULA], 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 underabundant. 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 2 Kpc 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.

Key words: stars: abundances – stars: individual: Sgr 143 – galaxies: abundances – galaxies: dwarf – galaxies: individual: Sgr dSPH

* Based on public data released from the UVES commissioning at the VLT Kueyen telescope, European Southern Observatory, Paranal, Chile.

Send offprint requests to: P. Bonifacio

Correspondence to: bonifaci@ts.astro.it

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© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000
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