I. Radial velocities and chemical abundances
European Southern Observatory, Casilla 19001, Santiago, Chile e-mail: firstname.lastname@example.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
Accepted: 27 October 2006
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 α-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 σ = 8.3 ± 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 [ α/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
Based on observations taken at ESO VLT Kueyen telescope (Cerro Paranal, Chile, program: 075.B-0127(A)) and 3.6 m telescope (La Silla, Chile). Also based on spectroscopic observations taken at the Telescopio Nazionale Galileo, operated by the Fundación G. Galilei of INAF at the Spanish Observatorio del Roque de los Muchachos of the IAC (La Palma, Spain).
© ESO, 2007