EDP Sciences
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Volume 465, Number 3, April III 2007
Page(s) 815 - 824
Section Galactic structure, stellar clusters, and populations
DOI http://dx.doi.org/10.1051/0004-6361:20066385

A&A 465, 815-824 (2007)
DOI: 10.1051/0004-6361:20066385

The exotic chemical composition of the Sagittarius dwarf spheroidal galaxy

L. Sbordone1, 2, 3, P. Bonifacio1, 2, 4, R. Buonanno5, 6, G. Marconi7, L. Monaco7, and S. Zaggia8

1  CIFIST Marie Curie Excellence Team, France
2  Observatoire de Paris, GEPI, 5 place Jules Janssen, 92195 Meudon, France
    e-mail: luca.sbordone@obspm.fr
3  INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Rome, Italy
4  INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
5  Università di Roma "Tor Vergata", via della Ricerca Scientifica 1, 00133 Rome, Italy
6  ASI Science Data Center, via Galileo Galilei, 00044 Frascati, Italy
7  ESO - European Southern Observatory, Alonso de Cordova, 3107 Santiago, Chile
8  INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padua, Italy

(Received 12 September 2006 / Accepted 29 November 2006)

Context.The Sagittarius dwarf spheroidal galaxy is the nearest neighbor of the Milky Way. Moving along a short period quasi-polar orbit within the Halo, it is being destroyed by the tidal interaction with our Galaxy, losing its stellar content along a huge stellar stream.
Aims.We study the detailed chemical composition of 12 giant stars in the Sagittarius dwarf Spheroidal main body, together with 5 more in the associated globular cluster Terzan 7 , by means of high resolution VLT-UVES spectra.
Methods.Abundances are derived for up to 21 elements from O to Nd, by fitting lines EW or line profiles against ATLAS 9 model atmospheres and SYNTHE spectral syntheses calculated ad-hoc. Temperatures are derived from (V-I)0 or (B-V)0 colors and gravities from $\ion{Fe}{i}$ - $\ion{Fe}{ii}$ ionization equilibrium.
Results.The metallicity of the observed stars is between [Fe/H] = -0.9 and 0. We detected a highly peculiar "chemical signature", with undersolar $\alpha$ elements, Na, Al, Sc, V, Co, Ni, Cu, and Zn, among others, and overabundant La, Ce, and Nd. Many of these abundance ratios (in particular light-odd elements and iron peak ones) are strongly at odds with what is observed within the Milky Way, so they may be a very useful tool for recognizing populations originating within the Sagittarius dwarf. This can be clearly seen in the case of the globular Palomar 12 , which is believed to have been stripped from Sagittarius: the cluster shows precisely the same chemical "oddities", thus finally confirming its extragalactic origin.

Key words: stars: abundances -- stars: atmospheres -- Galaxy: abundances -- galaxies: dwarf -- galaxies: individual: Sgr dSph -- Galaxy: globular clusters: individual: Terzan 7

© ESO 2007