We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 h of observations with the 4-m VISTA telescope during 5 years (2010-2014), covering ˜109 point sources across an area of 520 deg2, including 33 known globular clusters and ˜350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 μm) and a catalogue of more than 106 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium 1 , almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called "metallicity". A number of very metal poor stars have been found 2,3 , some of which, while having a low iron abundance, are rich in carbon, nitrogen and oxygen 4,5,6 . For theoretical reasons 7,8 and because of an observed absence of stars with metallicities lower than Z=1.5×10 5 , it has been suggested that low mass stars (M‹0.8M ⊙ , the ones that survive to the present day) cannot form until the interstellar medium has been enriched above a critical value, estimated to lie in the range 1.5×10 8 ≤Z≤1.5×10 6[8] , although competing * Gliese Fellow

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, gravities from Fe  -Fe  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 α 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, they thus may be a very useful tool to recognize populations originated 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.

We present the results of a thorough study of the nucleus of the Sgr dwarf spheroidal galaxy (Sgr dSph) and of the bright globular cluster M54 (NGC 6715) that resides within the same nucleus (Sgr,N). We have obtained accurate radial velocities and metallicity estimates for 1152 candidate Red Giant Branch stars of Sgr and M54 lying within ∼ 9 ′ from the center of the galaxy, from Keck/DEIMOS and VLT/FLAMES spectra of the infrared Calcium II triplet. Using both velocity and metallicity information we selected two samples of 425 and 321 very-likely members of M54 and of Sgr,N, respectively. The two considered systems display significantly different velocity dispersion profiles: M54 has a steeply decreasing profile from r = 0 ′ , where σ ≃ 14.2 km/s, to r ≃ 3 ′ .5 where it reaches σ ≃ 5.3 km/s, then it appears to rise again to σ ≃ 10 km/s at r ∼ 7 ′ . In contrast Sgr,N has a uniformly flat profile at σ ≃ 9.6 km/s over the whole 0 ′ ≤ r ≤ 9 ′ range. Using data from the literature we show that the velocity dispersion of Sgr remains constant at least out to r ∼ 100 ′ and there is no sign of the transition between the outer flat-luminosity-profile core and the inner nucleus in the velocity profile. These results -together with a re-analysis of the Surface Brightness profile of Sgr,N and a suite of dedicated N-body simulations -provide very strong support for the hypothesis that the nucleus of Sgr formed independently of M54, which probably plunged to its present position, coincident with Sgr,N, because of significant decay of the original orbit due to dynamical friction.

We develop, implement and characterise an enhanced data reduction approach which delivers precise, accurate, radial velocities from moderate resolution spectroscopy with the fibre-fed VLT/FLAMES+GIRAFFE facility. This facility, with appropriate care, delivers radial velocities adequate to resolve the intrinsic velocity dispersions of the very faint dSph dwarf galaxies. Importantly, repeated measurements let us reliably calibrate our individual velocity errors (0.2 ≤ δ V ≤ 5 km s −1 ) and directly detect stars with variable radial velocities. We show, by application to the Boötes I dwarf spheroidal, that the intrinsic velocity dispersion of this system is significantly below 6.5 km/s reported by previous studies. Our data favor a two-population model of Boötes I, consisting of a majority 'cold' stellar component, with velocity dispersion 2.4 +0.9 −0.5 km/s, and a minority 'hot' stellar component, with velocity dispersion ∼ 9 km/s, although we can not completely rule out a single component distribution with velocity dispersion 4.6 0.8 −0.6 km/s. We speculate this complex velocity distribution actually reflects the distribution of velocity anisotropy in Boötes I, which is a measure of its formation processes.