X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope (VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R ∼ 4000−17 000, depending on wavelength and slit width) with fixed échelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8 × 4 integral field unit as an alternative to the 11 long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.

This article presents a measurement of the proper motion of the Sculptor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope using the Space Telescope Imaging Spectrograph in the imaging mode. Each of two distinct fields contains a quasi-stellar object which serves as the "reference point." The measured proper motion of Sculptor, expressed in the equatorial coordinate system, is (µ α , µ δ ) = (9 ± 13, 2 ± 13) mas century −1 . Removing the

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The measured proper motion of Fornax, expressed in the equatorial coordinate system, is ( ; ) ¼ (47:6 AE 4:6; À36:0 AE 4:1) mas century À1 . This proper motion is a weighted mean of four independent measurements for three distinct fields. Each measurement uses a quasi-stellar object as a reference point. Removing the contribution of the motion of the Sun and of the local standard of rest to the measured proper motion produces a Galactic restframe proper motion of ( Grf ; Grf ) ¼ (24:4 AE 4:6; À14:3 AE 4:1) mas century À1 . The implied space velocity with respect to the Galactic center has a radial component of V r ¼ À31:8 AE 1:7 km s À1 and a tangential component of V t ¼ 196 AE 29 km s À1 . Integrating the motion of Fornax in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 118 (66, 137) and 152 (144, 242) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.13 (0.11, 0.38), and the orbital period is 3.2 (2.5, 4.6) Gyr. The orbit is retrograde and inclined by 101 (94 , 107 ) to the Galactic plane. Fornax could be a member of a proposed ''stream'' of galaxies and globular clusters; however, the membership of another proposed galaxy in the stream, Sculptor, has been previously ruled out. Fornax is in the Kroupa-Theis-Boily plane, which contains 11 of the Galactic satellite galaxies, but its orbit will take it out of that plane.

This article presents a measurement of the proper motion of the Ursa Minor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope in two distinct fields. Each field contains a quasi-stellar object that serves as the ''reference point.'' The measured proper motion for Ursa Minor, expressed in the equatorial coordinate system, is ( ; ) ¼ (À50 AE 17; 22 AE 16) mas century À1 . Removing the contributions of the solar motion and the motion of the local standard of rest yields the proper motion in the Galactic rest frame: ( Grf ; Grf ) ¼ (À8 AE 17; 38 AE 16) mas century À1 . The implied space velocity with respect to the Galactic center has a radial component of V r ¼ À75 AE 44 km s À1 and a tangential component of V t ¼ 144 AE 50 km s À1 . Integrating the motion of Ursa Minor in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 40 (10, 76) and 89 (78, 160) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.39 (0.09, 0.79), and the orbital period is 1.5 (1.1, 2.7) Gyr. The orbit is retrograde and inclined by 124 (94 , 136 ) to the Galactic plane. Ursa Minor is not a likely member of a proposed stream of galaxies on similar orbits around the Milky Way, nor is the plane of its orbit coincident with a recently proposed planar alignment of galaxies around the Milky Way. Comparing the orbits of Ursa Minor and Carina shows no reason for the different star formation histories of these two galaxies. Ursa Minor must contain dark matter to have a high probability of having survived disruption by the Galactic tidal force until the present.