Aims. In this paper we derive the structure of the Galactic stellar warp and flare. Methods. We use 2MASS red clump and red giant stars, selected at mean and fixed heliocentric distances of R 3, 7 and 17 kpc. Results. Our results can be summarized as follows: (i) a clear stellar warp signature is derived for the 3 selected rings, proving that the warp starts already within the solar circle; (ii) the derived stellar warp is consistent (both in amplitude and phase-angle) with that for the Galactic interstellar dust and neutral atomic hydrogen; (iii) the consistency and regularity of the stellar-gaseous warp is traced out to about R GC ∼ 20 kpc; (iv) the Sun seems not to fall on the line of nodes. The stellar warp phase-angle orientation (φ ∼ 15 • ) is close to the orientation angle of the Galactic bar and this, most importantly, produces an asymmetric warp for the inner R 3 and 7 kpc rings; (v) a Northern/Southern warp symmetry is observed only for the ring at R 17 kpc, at which the dependency on φ is weakened; (vi) treating a mixture of thin and thick disk stellar populations, we trace the variation with R GC of the disk thickness (flaring) and derive an almost constant scale-height (∼0.65 kpc) within R GC ∼ 15 kpc. Further out, the disk flaring increase gradually reaching a mean scale-height of ∼1.5 kpc at R GC ∼ 23 kpc; (vii) the derived outer disk warping and flaring provide further robust evidence that there is no disk radial truncation at R GC ∼ 14 kpc. Conclusions. In the particular case of the Canis Major (CMa) over-density we confirm its coincidence with the Southern stellar maximum warp occurring near l ∼ 240 • (for R 7 kpc) which brings down the Milky Way mid-plane by ∼3 • in this direction. The regularity and consistency of the stellar, gaseous and dust warp argues strongly against a recent merger scenario for Canis Major. We present evidence to conclude that all observed parameters (e.g. number density, radial velocities, proper motion etc) of CMa are consistent with it being a normal Milky Way outer-disk population, thereby leaving no justification for more complex interpretations of its origin. The present analysis or outer disk structure does not provide a conclusive test of the structure or origin of the Monoceros Ring. Nevertheless, we show that a warped flared Milky Way contributes significantly at the locations of the Monoceros Ring. Comparison of outer Milky Way H i and CO properties with those of other galaxies favors the suggestion that complex structures close to planar in outer disks are common, and are a natural aspect of warped and flaring disks.

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.

Aims. An interesting question of contemporary cosmology concerns the relation between the spatial distribution of galaxies and dark matter, which is thought to be the driving force behind the structure formation in the Universe. In this paper, we measure this relation, parameterised by the linear stochastic bias parameters, for a range of spatial scales using the data of the Garching-Bonn Deep Survey (GaBoDS). Methods. The weak gravitational lensing effect is used to infer matter density fluctuations within the field-of-view of the survey fields. This information is employed for a statistical comparison of the galaxy distribution to the total matter distribution. The result of this comparison is expressed by means of the linear bias factor b, the ratio of density fluctuations, and the correlation factor r between density fluctuations. The total galaxy sample is divided into three sub-samples using R-band magnitudes and the weak lensing analysis is applied separately for each sub-sample. Together with the photometric redshifts from the related COMBO-17 survey we estimate the typical mean redshifts of these samples withz = 0.35, 0.47, 0.61, respectively. Results. Using a flat ΛCDM model with Ω m = 0.3, Ω Λ = 0.7 as fiducial cosmology, we obtain values for the galaxy bias on scales between 1 ≤ θ ap ≤ 20 . At 10 , the median redshifts of the samples correspond roughly to a typical comoving scale of 3, 5, 7 h −1 Mpc with h = 0.7, respectively. We find evidence for a scale-dependence of b. Averaging the measurements of the bias over the range 2 ≤ θ ap ≤ 19 yieldsb = 0.81 ± 0.11, 0.79 ± 0.11, 0.81 ± 0.11 (1σ), respectively. Galaxies are thus less clustered than the total matter on that particular range of scales (anti-biased). As for the correlation factor r we see no scale-dependence within the statistical uncertainties; the average over the same range isr = 0.61 ± 0.16, 0.64 ± 0.18, 0.58 ± 0.19 (1σ), respectively. This implies a possible decorrelation between galaxy and dark matter distribution. An evolution of galaxy bias with redshift is not found, the upper limits are: ∆b 0.2 and ∆r 0.4(1σ).

Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. were not able to detect any iron lines, yet we could place a robust (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) < 1.8 for both stars. Conclusions. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas Article published by EDP Sciences A28, page 1 of 20 A&A 579, A28 (2015) cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.