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We present new homogeneous measurements of Na, Al, and three α-elements (Mg, Si, Ca) for 75 Galactic Cepheids. The abundances are based on high spectral resolution (R ~ 38 000) and high signal-to-noise ratio (S/N ∼ 50-300) spectra collected with UVES at ESO VLT. The current measurements were complemented with Cepheid abundances provided by our group (75) or available in the literature, for a total of 439 Galactic Cepheids. Special attention was given to providing a homogeneous abundance scale for these five elements plus iron. In addition, accurate Galactocentric distances (RG) based on near-infrared photometry are also available for all the Cepheids in the sample. They cover a large section of the Galactic thin disk (4.1 ≤ RG ≤ 18.4 kpc). We found that these five elements display well-defined linear radial gradients and modest standard deviations over the entire range of RG. Moreover, the [element/Fe] abundance ratios are constant across the entire thin disk; only the Ca radial distribution shows marginal evidence of a positive slope. These results indicate that the chemical enrichment history of iron and of the quoted five elements has been quite similar across the four quadrants of the Galactic thin disk. The [element/Fe] ratios are also constant over the entire period range. This empirical evidence indicates that the chemical enrichment of Galactic Cepheids has also been very homogenous within the range in age that they cover (~10-300 Myr). Once again, [Ca/Fe] vs. log P shows a (negative) gradient, since it is underabundant among the youngest Cepheids. Finally, we also find that Cepheid abundances agree quite well with similar abundances for thin and thick disk dwarf stars, and they follow the typical Mg-Al and Na-O correlations. [ABSTRACT FROM AUTHOR]

We have performed a new abundance analysis of Carina red giant (RG) stars from spectroscopic data collected with UVES (high spectral resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high-resolution) and 800 (medium-resolution) RGs, covering a significant fraction of the galaxy's RG branch, and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and e ective temperature bins. The spectra of the stars belonging to the same gravity and temperature bin were stacked. This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit (V ⩾ 20.5 mag) by at least a factor of five. We took advantage of the new photometry index cU,B,J introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean iron abundances are -2:15 ± 0:06 dex (σ = 0:28), and 1:75 ± 0:03 dex (σ = 0:21), respectively. The two iron distributions di er at the 75% level. This supports preliminary results. Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of -1:91 ± 0:05 dex (σ = 0:22) and 1:35±0:03 dex ( σ= 0:22); these di er at the 83% level. Carina's -element abundances agree, within 1σ, with similar abundances for field halo stars and for cluster (Galactic and Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite di erent from that in the globular clusters. [ABSTRACT FROM AUTHOR]

Context. Discovered in the last decade as overdensities of resolved stars, the ultra-faint dwarfs (UFDs) are among the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They appear as sparse, loose objects with high mass-to-light ratios. Hercules is the prototype of the UFD galaxies. To date, there are still no firm constraints on its total luminosity due to the difficulty of disentangling Hercules bona-fide stars from the severe Galactic field contamination. Aims. To better constrain Hercules properties, we aim at removing foreground and background contaminants in the galaxy field using the proper motions of the Milky Way stars and the colour-colour diagram. Methods. We have obtained images of Hercules in the rSloan, BBessel and Uspec bands with the Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The rSloan new dataset combined with data from the LBT archive span a time baseline of about 5 yr, allowing us to measure proper motions of stars in the Hercules direction for the first time. The Uspec data along with existing LBT photometry allowed us to use colour-colour diagram to further remove the field contamination. Results. Thanks to a highly-accurate procedure to derive the rSloan-filter geometric distortion solution for the LBC-red, we were able to measure stellar relative proper motions to a precision of better than 5 mas yr-1 down to rSloan ≈ 22 mag and disentangle a significant fraction (>90%) of MilkyWay contaminants. We ended up with a sample of 528 sources distributed over a large portion of the galaxy body (∼0.12 deg2). Of these sources, 171 turned out to be background galaxies and additional foreground stars from the analysis of the Uspec - BBessel vs. BBessel - rSloan colour-colour diagram. This leaves us with a sample of 357 likely members of the Hercules UFD. We compared the cleaned colour-magnitude diagram (CMD) with evolutionary models and synthetic CMDs, confirming the presence in Hercules of an old population (t = 12 ± 2 Gyr) with wide spread metallicity (-3:3 < [Fe/H] < -1:8). Conclusions. Our procedure to estimate star proper motions proved to be a very effective way to identify likely members for stellar systems as far as 130 kpc. The present selection, based on both proper motions and colour-colour diagram, provides a robust identification of Hercules members and a new target list for more spectroscopic investigations. [ABSTRACT FROM AUTHOR]

NGC 1851 is surrounded by a stellar component that extends more than 10 times beyond the tidal radius. Although the nature of this stellar structure is not known, it has been suggested to be a sparse halo of stars or associated with a stellar stream. We analyse the nature of this intriguing stellar component surrounding NGC 1851 by investigating its radial velocities and chemical composition, in particular in comparison with those of the central cluster analysed in a homogeneous manner. In total we observed 23 stars in the halo with radial velocities consistent with NGC 1851, and for 15 of them we infer [Fe/H] abundances. Our results show that (i) stars dynamically linked to NGC 1851 are present at least up to ∼2.5 tidal radii, supporting the presence of a halo of stars surrounding the cluster; (ii) apart from the NGC 1851 radial velocity-like stars, our observed velocity distribution agrees with that expected from Galactic models, suggesting that no other substructure (such as a stream) at different radial velocities is present in our field; (iii) the chemical abundances for the s-process elements Sr and Ba are consistent with the s-normal stars observed in NGC 1851; (iv) all halo stars have metallicities, and abundances for the other studied elements Ca, Mg and Cr, consistent with those exhibited by the cluster. The complexity of the whole NGC 1851 cluster+halo system may agree with the scenario of a tidally disrupted dwarf galaxy in which NGC 1851 was originally embedded. [ABSTRACT FROM PUBLISHER]

We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high resolution (R ~ 38 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra collected with UVES at VLT (128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We were careful to derive a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated accurate individual distances for the entire sample by using homogeneous near-infrared photometry and the reddening free period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (RG ~ 5–19 kpc) and agrees quite well with similar estimates available in the literature (–0.060 ± 0.002 dex/kpc). We also uncover evidence that suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and also for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyr, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity, and distance scales. Finally, by using a large sample of Galactic and Magellanic Cepheids for which accurate iron abundances are available, we found that the dependence of the luminosity amplitude on metallicity is vanishing. [ABSTRACT FROM AUTHOR]

We present Strömgren and near-infrared (NIR) photometry of the bulge cluster NGC 6528 and its surrounding field in Baade’s Window. uvby images were collected with EFOSC2 on the New Technology Telescope (NTT, La Silla, ESO). The NIR catalogs are based on J, K-band VIRCAM at VISTA (Paranal, ESO) and SOFI at NTT photometry. We matched the aforementioned data sets with Hubble Space Telescope photometry to obtain proper-motion-cleaned samples of NGC 6528 and bulge stars. Furthermore, we were able to correct the Strömgren-NIR photometry for differential reddening. The huge color sensitivity of the Strömgren-NIR color–magnitude-diagrams (CMDs) helped us in separating age and metallicity effects. The red giant branch (RGB) of NGC 6528 is well reproduced in all the CMDs by adopting scaled solar isochrones with solar abundance, that is Z = 0.0198, or α-enhanced isochrones with the same iron content, that is Z = 0.04, and an age range of t = 10–12 Gyr. The same isochrones well reproduce most of the color spread of Baade’s Window RGB. These findings support the literature age estimates for NGC 6528. We also performed a new theoretical visual-NIR metallicity calibration based on the Strömgren index m1 and on visual–NIR colors for red giant (RG) stars. Scaled solar and α-enhanced models were adopted and we validated the new metallicity-index-color (MIC) relations by applying them to estimate the photometric metal abundance of a sample of field RGs and of a metal-poor (M 92, [Fe/H] ∼ −2.3) and a metal-rich (NGC 6624, [Fe/H] ∼ −0.7) globular cluster. We applied the calibration to estimate the mean metal abundance of NGC 6528, finding [Fe/H] = [M/H] = −0.04 ± 0.02, with a mean intrinsic dispersion of σ = 0.27 dex, by averaging the metallicities obtained with the scaled solar [m], y− J and [m], y− K MIC relations, and of −0.11± 0.01, with σ = 0.27 dex, by using the m1, y − J and m1, y − K relations. These findings support results based on high-resolution spectroscopy, which approximately give a solar metallicity for NGC 6528 with a modest α-enhancement. By applying the scaled solar MIC relations to the sample of Baade’s Window RGs, we find a metallicity distribution that extends approximately from [Fe/H] ∼ −1.0 up to [Fe/H] ∼ 1 dex, with two metallicity peaks at [Fe/H] ≈ −0.2 and [Fe/H] ≈ 0.55 ([m], y− J and [m], y− K relations), and [Fe/H] ≈ −0.25 and [Fe/H] ≈ 0.4 (m1, y− J and m1, y−K relations). These findings fairly agree with previous spectroscopic studies for Baade’sWindow and the recent results of the ARGOS surveys for the bulge. [ABSTRACT FROM AUTHOR]

We used Hubble Space Telescope observations to study the young cluster NGC 1844 in the Large Magellanic Cloud (LMC). We estimated the fraction and the mass-ratio distribution of photometric binaries and report that the main sequence presents an intrinsic breadth which cannot be explained only in terms of photometric errors, and is unlikely because of differential reddening.We attempted different interpretations of this feature, including stellar rotation, binary stars, and the presence of multiple stellar populations of different ages, metallicity, helium, or C+N+O abundance. Although we have excluded age, helium, and C+N+O variations of being responsible for the main-sequence spread, none of the other interpretations is conclusive. [ABSTRACT FROM AUTHOR]

On the basis of a new photometric analysis of the Local Group dwarf irregular galaxy NCG 6822 based on observations obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Because of significant differences in the distance estimates to NGC 6822 available in literature, we decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the red giant branch brightness. As a result we newly determined the distance to NGC 6822 to be equal to (m - M)0 = 23.54 ± 0.05, and compared our measurement with the most recent determinations of this distance. [ABSTRACT FROM AUTHOR]

We devised a new method to estimate globular cluster absolute ages by adopting the knee of the bending of the lower main-sequence (MS) in the Near-Infrared (NIR) J, J - Ks color-magnitude diagram. The color difference between this feature and the Turn-Off point is strongly correlated to the cluster age. This method is marginally affected by distance and reddening uncertainties, and by the possible occurrence of differential reddening. Furthermore, the knee location does not depend on the cluster age and it is a robust theoretical prediction. We adopted accurate J, Ks-band photometry collected with both MAD/VLT and SOFI/NTT for the Galactic globular cluster NGC 3201 to identify the location of the knee at J~19.90 ±0.03 and J-Ks ~0.76±0.02 mag. The comparison with different sets of cluster isochrones, transformed adopting different Color–Temperature–Relations (CTRs), shows that the models are slightly redder than the observations for J > 19 mag. This difference could be due to the presence of a calibration drift or to a problem of the CTRs in this magnitude range. [ABSTRACT FROM PUBLISHER]

We adopted uvby Strömgren photometry to investigate the metallicity distribution of ω Cen Red Giant (RG) stars. We provided a new empirical calibration of the Strömgren m1≡(v − b) − (b − y) metallicity index based on cluster stars. The new calibration has been applied to a sample of ω Cen RGs. The shape of the estimated metallicity distribution is clearly asymmetric, with a sharp cut-off at low metallicities ([Fe/H] < −2.0) and a metal-rich tail up to [Fe/H] ∼ 0.0. Two main metallicity peaks have been identified, around [Fe/H]≈ −1.9 and −1.3 dex, and a metal-rich shoulder at ≈ −0.2 dex. [ABSTRACT FROM PUBLISHER]

ABSTRACTWe present the first results of a large photometric survey devoted to the study of the star formation history of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three wide strips (size ∼ 9 × 35 arcmin 2) located at ∼ (l ° b °) = (6.5;-16), (6;-14), (5;-12) have been observed. Each strip is roughly east--west oriented, nearly along the major axis of the galaxy. A control field (size ∼ 9 × 24 arcmin 2), located outside the body of Sgr dSph [∼ (l ° b °) = (354;-14)] has also been observed for statistical decontamination purposes. Accurate and well-calibrated V, I photometry down to V ∼ 22 has been obtained for ∼ 90 000 stars towards the Sgr dSph and ∼ 8000 stars in the control field. This is the largest photometric sample (covering the widest spatial extension) ever observed in the Sgr dSph up to now. The main new results presented in this paper are: (1) the possible discovery of a strong asymmetry in the distribution of stars along the major axis, since the north-western arm of the Sgr galaxy (i.e. the region nearer to the Galactic bulge) apparently shows a significant deficiency of Sgr stars and (2) the first direct detection of a very metal-poor (and presumably old) population in the Sgr stellar content. Hints at a metallicity gradient towards the densest region of the galaxy are also reported. [ABSTRACT FROM AUTHOR]

A detailed study of the star formation history of the Sagittarius dwarf spheroidal galaxy is performed through the analysis of data from the Sagittarius Dwarf Galaxy Survey (SDGS). Accurate statistical decontamination of the SDGS colour–magnitude diagrams (CMDs) allows us to obtain many useful constraints on the age and metal content of the Sgr stellar populations in three different regions of the galaxy. A coarse metallicity distribution of Sgr stars is derived, ranging from [Fe/H]∼-2.0 to [Fe/H]∼-0.7, the upper limit being somewhat higher in the central region of the galaxy. A qualitative global fit to all the observed CMD features is attempted, and a general scheme for the star formation history of the Sgr dSph is derived. According to this scheme, star formation began at a very early time from a low metal content interstellar medium and lasted for several Gyr, coupled with progressive chemical enrichment. The star formation rate (SFR) had a peak from 8 to 10 Gyr ago, when the mean metallicity was in the range -1.3≤[Fe/H]≤-0.7. After that maximum, the SFR rapidly decreased and a very low rate of star formation took place until ∼1–0.5 Gyr ago. [ABSTRACT FROM AUTHOR]

The new generation of astronomical detectors based on Superconducting Tunnel Junctions (STJs) is capable of detecting photons in a wide range of wavelengths, and, in some cases, even of counting single photons. Since these detectors operate at very low temperature (down to 100 mK), a natural candidate for the readout electronics is the dc-SQUID, a superconducting device that can work as a current preamplifier, reaching very good noise performance. In this paper we present measurements on a homemade dc-SQUID, showing the response of the device to small current pulses, which simulate the real signals from an STJ. An optimal filtering processing of the data is performed, in order to extract from the noisy data the best estimate for the pulse height, which, in a real experiment with single optical photons, would be the parameter that carries the spectroscopic information. [ABSTRACT FROM AUTHOR]

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We present the radial velocity (RV) distribution of Carina dSph, obtained using low-, medium- and high-resolution spectroscopic data collected with FORS2 and GIRAFFE at the VLT. We found that regions where the mean RV is smaller the dispersion is also smaller, and the RV distribution is sharper (i.e. the kurtosis attains larger values). The mean RV, when moving to lower Galactic latitude, decreases by ~5 km s-1, attains a well defined minimum outside the galaxy center, and a constant value at larger distances. The RV gradient appears to be in the direction of the Carina proper motion. However, this parameter is affected by large uncertainties to reach a firm conclusion. These findings are probably reminiscent of a substructure with transition properties, already detected in dwarf ellipticals, and call for independent confirmations. [ABSTRACT FROM AUTHOR]

Multi-object spectrographs available on 8-m class telescopes provide the unique opportunity to directly investigate the kinematical and chemical properties of significant samples of resolved stars in galaxies of the Local Group. We present here the first results concerning an extensive study of stellar populations of the Carina dSph galaxy, based on data collected with the multi-object spectrographs FORS2 and FLAMES, both available at VLT. Preliminary estimates concerning the radial velocity distributions of the different samples are presented. [ABSTRACT FROM PUBLISHER]

We present new near-infrared Ks photometry of the interesting Galactic globular cluster NGC 6441. The optical-NIR color-magnitude diagram shows evolutionary features that seem to agree with a canonical evolutionary framework. The K-band Period-Luminosity-Metallicity relation of RR Lyrae stars gives a distance estimate of 15.51±0.07 that is slightly larger previous estimates. [ABSTRACT FROM PUBLISHER]

ABSTRACTWe present the first results of a large photometric survey devoted to the study of the star formation history of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three wide strips (size ∼ 9 × 35 arcmin 2) located at ∼ (l ° b °) = (6.5;-16), (6;-14), (5;-12) have been observed. Each strip is roughly east--west oriented, nearly along the major axis of the galaxy. A control field (size ∼ 9 × 24 arcmin 2), located outside the body of Sgr dSph [∼ (l ° b °) = (354;-14)] has also been observed for statistical decontamination purposes. Accurate and well-calibrated V, I photometry down to V ∼ 22 has been obtained for ∼ 90 000 stars towards the Sgr dSph and ∼ 8000 stars in the control field. This is the largest photometric sample (covering the widest spatial extension) ever observed in the Sgr dSph up to now. The main new results presented in this paper are: (1) the possible discovery of a strong asymmetry in the distribution of stars along the major axis, since the north-western arm of the Sgr galaxy (i.e. the region nearer to the Galactic bulge) apparently shows a significant deficiency of Sgr stars and (2) the first direct detection of a very metal-poor (and presumably old) population in the Sgr stellar content. Hints at a metallicity gradient towards the densest region of the galaxy are also reported. [ABSTRACT FROM AUTHOR]