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Issue A&A
Volume 464, Number 1, March II 2007
Page(s) 201 - 209
Section Galactic structure, stellar clusters, and populations
DOI http://dx.doi.org/10.1051/0004-6361:20066228



A&A 464, 201-209 (2007)
DOI: 10.1051/0004-6361:20066228

High-resolution spectroscopy of RGB stars in the Sagittarius streams

I. Radial velocities and chemical abundances
L. Monaco1, M. Bellazzini2, P. Bonifacio3, 4, 5, A. Buzzoni2, F. R. Ferraro6, G. Marconi1, L. Sbordone5, 7, and S. Zaggia8

1  European Southern Observatory, Casilla 19001, Santiago, Chile
    e-mail: lmonaco@eso.org
2  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Bologna, 40127 Bologna, Italy
3  CIFIST Marie Curie Excellence Team
4  Observatoire de Paris, GEPI, 5 place Jules Janssen, 92195 Meudon, France
5  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
6  Università di Bologna - Dipartimento di Astronomia, 40127 Bologna, Italy
7  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
8  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy

(Received 11 August 2006 / Accepted 27 October 2006)

Abstract
Context.The Sagittarius (Sgr) dwarf spheroidal galaxy is currently being disrupted under the strain of the Milky Way. A reliable reconstruction of Sgr star formation history can only be obtained by combining core and stream information.
Aims.We present radial velocities for 67 stars belonging to the Sgr Stream. For 12 stars in the sample we also present iron (Fe) and $\alpha$-element (Mg, Ca) abundances.
Methods.Spectra were secured using different high resolution facilities: UVES@VLT, HARPS@3.6 m, and SARG@TNG. Radial velocities are obtained through cross correlation with a template spectra. Concerning chemical analysis, for the various elements, selected line equivalent widths were measured and abundances computed using the WIDTH code and ATLAS model atmospheres.
Results.The velocity dispersion of the trailing tail is found to be $\sigma$ = 8.3 $\pm$ 0.9 km s-1, i.e., significantly lower than in the core of the Sgr galaxy and marginally lower than previous estimates in the same portion of the stream. Stream stars follow the same trend as Sgr main body stars in the [ $\alpha$/Fe]  vs. [Fe/H] plane. However, stars are, on average, more metal poor in the stream than in the main body. This effect is slightly stronger in stars belonging to more ancient wraps of the stream, according to currently accepted models of Sgr disruption.


Key words: stars: abundances -- stars: atmospheres -- galaxies: abundances -- galaxies: evolution -- galaxies: dwarf -- galaxies: individual: Sgr dSph



© ESO 2007


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