Search

We analyze a sample of 4500 photometrically-selected Ha emitter galaxies at redshifts z~2 and z~4-6 selected from James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) medium-band images in the Great Observatories Origins Deep Survey South (GOODS-S). The bulk (80%) of the galaxies in our sample have stellar masses lower than 10^8 Msun, with a median stellar mass of ~10^7.3 Msun. We derive Ha rest-frame equivalent widths ( EW0(Ha) ), line fluxes, and star formation rates using a robust photometric excess technique tested against spectroscopic measurements, being sensitive to EW0(Ha) > 75 A. Both EW0(Ha) and sSFR(Ha) anti-correlate with stellar mass, and at fixed stellar mass, show a steep increasing trend with redshift sSFR(Ha) ~ (1+z)^2.55. By comparing the Ha and rest-frame UV-derived SFRs, we probe the star formation histories (SFHs) of our galaxies in the past 100 Myr. The fraction of low-mass galaxies (M < 10^8 Msun) with signs of bursty star formation from their SFR(Ha)/SFR(UV) is ~ 50 %. It quickly drops to ~ 25 % for M > 10^8 Msun. This is consistent with the results from sSFR(Ha), showing 80% and 17%, respectively. SFR(Ha)/SFR(UV) is a stricter criterion than those based on the galaxy sSFR(Ha), as it only identifies the strongest starbursts, the ones at the initial phases of a bursty star-formation episode., Comment: 20 pages, 10 figures. Submitted to ApJ, comments are welcome

We investigate the correlation between stellar mass (M*) and star formation rate (SFR) across the stellar mass range log10(M*/Msun)~6-11. We consider almost 50,000 star-forming galaxies at z~3-7, leveraging data from COSMOS/SMUVS, JADES/GOODS-SOUTH, and MIDIS/XDF. This is the first study spanning such a wide stellar mass range without relying on gravitational lensing effects. We locate our galaxies on the SFR-M* plane to assess how the location of galaxies in the star-formation main sequence (MS) and starburst (SB) region evolves with stellar mass and redshift. We find that the two star-forming modes tend to converge at log10(M*/Msun) < 7, with all galaxies found in the SB mode. By dissecting our galaxy sample in stellar mass and redshift, we show that the emergence of the star-formation MS is stellar-mass dependent: while in galaxies with log10(M*/Msun) > 9 the MS is already well in place at z = 5-7, for galaxies with log10(M*/Msun)~7-8 it only becomes significant at z<4. Overall, our results are in line with previous findings that the SB mode dominates amongst low stellar-mass galaxies. The earlier emergence of the MS for massive galaxies is consistent with galaxy downsizing., Comment: 15 pages, 4 figures. Submitted to ApJ

Context. Open clusters provide valuable information on stellar nucleosynthesis and the chemical evolution of the Galactic disc, as their age and distances can be measured more precisely with photometry than for field stars. Aims. Our aim is to study the chemical distribution of the Galactic disc using open clusters by analysing the existence of gradients with Galactocentric distance, azimuth or height from the plane and dependency with age. Methods. High-resolution spectra (R>60 000) of 194 stars belonging to 36 open clusters are used to determine atmospheric parameters and chemical abundances with two independent methods: equivalent widths and spectral synthesis. The sample has been complemented with 63 clusters with high-resolution spectroscopy from literature. Results. We measure local thermodynamic equilibrium abundances for 21 elements: {\alpha} (Mg, Si, Ca, and Ti), odd-Z (Na and Al), Fe-peak (Fe, Sc, V, Cr, Mn, Co, Ni, Cu, and Zn), and neutron-capture (Sr, Y, Zr, Ba, Ce, and Nd). We also provide non-local thermodynamic equilibrium abundances for elements when corrections are available. We find inner disc young clusters enhanced in [Mg/Fe] and [Si/Fe] compared to other clusters of their age. For [Ba/Fe] we report an age trend flattening for older clusters (age<2.5 Ga). The studied elements follow the expected radial gradients as a function of their nucleosynthesis groups, which are significantly steeper for the oldest systems. For the first time, we investigate the existence of an azimuthal gradient, finding some hints of its existence among the old clusters (age>2 Ga).

Context: Open clusters' dynamical evolution is driven by stellar evolution, internal dynamics and external forces, which according to dynamical simulations, will evaporate them in a timescale of about 1 Ga. However, about 10\% of the known open clusters are older. They are special systems whose detailed properties are related to their dynamical evolution and the balance between mechanisms of cluster formation and dissolution. Aims:We investigate the spatial distribution and structural parameters of six open clusters older than 1 Ga in order to constrain their dynamical evolution, and longevity.} Methods: We identify members using Gaia EDR3 data up to a distance of 150 pc from each cluster's centre. We investigate the spatial distribution of stars inside each cluster to understand their degree of mass segregation. Finally, in order to interpret the obtained radial density profiles we reproduced them using the lowered isothermal model explorer with PYTHON Limepy and spherical potential escapers stitched SPES. Results: All the studied clusters seem more extended than previously reported in the literature. The spatial distributions of three of them show some structures aligned with their orbits. They may be related to the existence of extra tidal stars. In fact, we find that about 20 % of their members have enough energy to leave the systems or are already unbound. Together with their initial masses, their distances to the Galactic plane may play significant roles in their survival. We found clear evidences that the most dynamically evolved clusters do not fill their Roche volumes, appearing more concentrated than the others. Finally, we find a cusp-core dichotomy in the central regions of the studied clusters, which shows some similarities to the one observed among globular clusters., Comment: 16 pages, 11 figures, accepted for publication in A&A

We make use of \textit{JWST} medium and broad-band NIRCam imaging, along with ultra-deep MIRI $5.6 \rm \mu m$ imaging, in the Hubble eXtreme Deep Field (XDF) to identify prominent line emitters at $z\simeq 7-8$. Out of a total of 58 galaxies at $z\simeq 7-8$, we find 18 robust candidates ($\simeq$31\%) for (H$\beta$ + [OIII]) emitters, based on their enhanced fluxes in the F430M and F444W filters, with EW$_{0}$(H$\beta$ +[OIII]) $\simeq 87 - 2100$ {\AA}. Among these emitters, 16 lie in the MIRI coverage area and 12 exhibit a clear flux excess at $5.6 \, \rm \mu m$, indicating the simultaneous presence of a prominent H$\alpha$ emission line with EW$_{0}$(H$\alpha$) $\simeq 200-3000$ {\AA}. This is the first time that H$\alpha$ emission can be detected in individual galaxies at $z>7$. The H$\alpha$ line, when present, allows us to separate the contributions of H$\beta$ and [OIII] to the (H$\beta$ +[OIII]) complex, and derive H$\alpha$-based star formation rates (SFRs). We find that in most cases [OIII]/H$\beta > 1$. Instead, two galaxies have [OIII]/H$\beta < 1$, indicating that the NIRCam flux excess is mainly driven by H$\beta$. This could potentially imply extremely low metallicities. Most prominent line emitters are very young starbursts or galaxies on their way to/from the starburst cloud. They make for a cosmic SFR density $\rm log_{10}(\rho_{SFR_{H\alpha}}) \simeq -2.35$, which is about a quarter of the total value ($\rm log_{10}(\rho_{SFR_{tot}}) \simeq -1.76$) at $z\simeq 7-8$. Therefore, the strong H$\alpha$ emitters likely had a significant role in reionization., Comment: 18 pages, 11 figures. The paper has been accepted for publication in ApJ

Exploring the Galactic chemical evolution and enrichment scenarios with open clusters allows us to understand the history of the Milky Way disk. High-resolution spectra of OCs are a crucial tool, as they provide precise chemical information, to combine with precise distances and ages. The aim of the Stellar Population Astrophysics project is to derive homogeneous and accurate comprehensive chemical characterization of a number of poorly studied OCs.Using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo, we obtained high-resolution spectra of giant stars in 18 OCs, 16 of which are chemically characterized for the first time, and two of which are well studied for comparison. The OCs in this sample have ages from a few tens of Myr to 4 Gyr, with a prevalence of young clusters. We already presented the radial velocities and atmospheric parameters for them in a previous SPA paper. Here, we present results for the alpha-elements O, and the light elements, all determined by the equivalent width method. We also measured Li abundance through the synthesis method.We discuss the behaviors of lithium, sodium and aluminum in the context of stellar evolution. We study the radial, vertical, and age trends for the measured abundance ratios in a sample that combines our results and recent literature for OCs, finding significant gradients only for [Mg/Fe] and [Ca/Fe] in all cases. Finally,we compare O and Mg in the combined sample with chemo-dynamical models, finding a good agreement for intermediate-age and old clusters. There is a sharp increase in the abundance ratios measured among very young clusters, accompanied by a poorer fit with the models for O and Mg, likely related to the inadequacy of traditional model atmospheres and methods in the derivation of atmospheric parameters and abundance ratios for stars of such young ages

Context: Open clusters are ideal laboratories to investigate a variety of astrophysical topics, from the properties of the Galactic disc to stellar evolution models. For this purpose, we need to know their chemical composition in detail. Unfortunately, the number of systems with chemical abundances determined from high resolution spectroscopy remains small. Aims: Our aim is to increase the number of open clusters with radial velocities and chemical abundances determined from high resolution spectroscopy by sampling a few stars in clusters not studied previously. Methods: We obtained high resolution spectra with the FIES spectrograph at NOT for 41 stars belonging to 20 open clusters. These stars have high astrometric membership probabilities, determined from the Gaia second data release. Results: We derived radial velocities for all the observed stars, which were used to confirm their membership to the corresponding clusters. For Gulliver\,37 we cannot be sure the observed star is a real member. We derived atmospheric parameters for the 32 stars considered real cluster members. We discarded five stars because they have very low gravity or atmospheric parameters were not properly constrained due to low signal-to-noise ratio spectra. Therefore, detailed chemical abundances were determined for 28 stars belonging to 17 clusters. For most of them, this is the first chemical analysis available in the literature. Finally, we compared the clusters in our sample to a large population of well studied clusters. The studied systems follow the trends, both chemical and kinematical, described by the majority of open clusters. Worth noticing that the three most metal-poor studied clusters (NGC\,1027, NGC\,1750 and Trumpler 2) are enhanced in Si but not in the other alpha-elements studied (Mg, Ca and Ti)., Comment: 19 pages Accepted for publication on A&A

Context: Open clusters (OCs) are widely used as test particles to investigate a variety of astrophysical phenomena, from stellar evolution to Galactic evolution. Gaia and the complementary massive spectroscopic surveys are providing an unprecedented wealth of information about these systems. Aims: The Open Cluster Chemical Abundances from Spanish Observatories (OCCASO) survey aims to complement all this work by determining OCs accurate radial velocities and chemical abundances from high-resolution, R$\geq$60\,000, spectra. Methods: Radial velocities have been obtained by cross-correlating the observed spectra with a library of synthetic spectra which covers from early M to A spectral types. Results: We provide radial velocities for 336 stars, including several Gaia Benchmark Stars and objects belonging to 51 open clusters. The internal uncertainties of the derived radial velocities go from 10 m/s to 21 m/s as a function of the instrumental configuration used. The derived radial velocities, together with the Gaia proper motions, have been used to investigate the cluster membership of the observed stars. After this careful membership analysis, we obtain average velocities for 47 open clusters. To our knowledge, this is the first radial velocity determination for 5 of these clusters. Finally, the radial velocities, proper motions, distances and ages have been used to investigate the kinematics of the observed clusters and in the integration of their orbits., Comment: 27 pages, accepted for publication in A&A

Stock 2 is a little-studied open cluster that shows an extended main-sequence turnoff (eMSTO). In order to investigate this phenomenon and characterise the cluster itself we performed high-resolution spectroscopy in the framework of the Stellar Population Astrophysics (SPA) project. We employed the High Accuracy Radial velocity Planet Searcher in North hemisphere spectrograph (HARPS-N) at the Telescopio Nazionale Galileo (TNG). We completed our observations with additional spectra taken with the Catania Astrophysical Observatory Spectrograph (CAOS). In total we observed 46 stars (dwarfs and giants), which represent, by far, the largest sample collected for this cluster to date. We provide the stellar parameters, extinction, radial and projected rotational velocities for most of the stars. Chemical abundances for 21 species with atomic numbers up to 56 have also been derived. We notice a differential reddening in the cluster field whose average value is 0.27 mag. It seems to be the main responsible for the observed eMSTO, since it cannot be explained as the result of different rotational velocities, as found in other clusters. We estimate an age for Stock 2 of 450$\pm$150 Ma which corresponds to a MSTO stellar mass of $\approx$2.8 M$_{\odot}$. The cluster mean radial velocity is around 8.0 km s$^{-1}$. We find a solar-like metallicity for the cluster, [Fe/H]=$-$0.07$\pm$0.06, compatible with its Galactocentric distance. MS stars and giants show chemical abundances compatible within the errors, with the exceptions of Barium and Strontium, which are clearly overabundant in giants, and Cobalt, which is only marginally overabundant. Finally, Stock 2 presents a chemical composition fully compatible with that observed in other open clusters of the Galactic thin disc., Comment: Accepted for publication in Astronomy and Astrophysics; 18 pages, 13 figures, 12 tables

Thanks to modern understanding of stellar evolution, we can accurately measure the age of Open Clusters (OCs). Given their position, they are ideal tracers of the Galactic disc. Gaia data release 2, besides providing precise parallaxes, led to the detection of many new clusters, opening a new era for the study of the Galactic disc. However, detailed information on the chemical abundance for OCs is necessary to accurately date them and to efficiently use them to probe the evolution of the disc.Mapping and exploring the Milky Way structure %to combine accurate chemical information of OCs is the main aim of the Stellar Population Astrophysics (SPA) project. Part of this work involves the use of OCs and the derivation of their precise and accurate chemical composition.We analyze here a sample of OCs located within about 2 kpc from the Sun, with ages from about 50 Myr to a few Gyr.We used HARPS-N at the Telescopio Nazionale Gaileo and collected very high-resolution spectra (R = 115\,000) of 40 red giant/red clump stars in 18 OCs (16 never or scarcely studied plus two comparison clusters). We measured their radial velocities and derived the stellar parameters.We discussed the relationship between metallicity and Galactocentric distance, adding literature data to our results to enlarge the sample and taking also age into account. We compared the result of observational data with that from chemo-dynamical models. These models generally reproduce the metallicity gradient well. However, at young ages we found a large dispersion in metallicity, not reproduced by models. Several possible explanations are explored, including uncertainties in the derived metallicity. We confirm the difficulties in determining parameters for young stars (age < 200 Myr), due to a combination of intrinsic factors which atmospheric models can not easily reproduce and which affect the parameters uncertainty, Comment: 21 pages 9 figures Astronomy & Astrophysics

Context: Precise chemical abundances coupled with reliable ages are key ingredients to understand the chemical history of our Galaxy. Open Clusters (OCs) are useful for this purpose because they provide ages with good precision. Aims: The aim of this work is to investigate the relations of different chemical abundance ratios vs age traced by red clump (RC) stars in OCs. Methods: We analyze a large sample of 209 reliable members in 47 OCs with available high-resolution spectroscopy. We applied a differential line-by-line analysis to provide a comprehensive chemical study of 25 chemical species. This sample is among the largest samples of OCs homogeneously characterized in terms of atmospheric parameters, detailed chemistry, and ages. Results: In our metallicity range (-0.2<[M/H]<+0.2) we find that while most Fe-peak and alpha elements have flat dependence with age, the s-process elements show decreasing trends with increasing age with a remarkable knee at 1 Gyr. For Ba, Ce, Y, Mo and Zr we find a plateau at young ages (< 1 Gyr). We investigate the relations of all possible combinations among the computed chemical species with age. We find 19 combinations with significant slopes, including [Y/Mg] and [Y/Al]. The ratio [Ba/alpha] is the one with the most significant correlations found. Conclusions: We find that the [Y/Mg] relation found in the literature using Solar twins is compatible with the one found here in the Solar neighbourhood. The age-abundance relations show larger scatter for clusters at large distances (d>1 kpc) than for the Solar neighbourhood, particularly in the outer disk. We conclude that these relations need to be understood also in terms of the complexity of the chemical space introduced by the Galactic dynamics, on top of pure nucleosynthetic arguments, especially out of the local bubble., Comment: Accepted for publication in A&A

Open Clusters (OCs) can trace with a great accuracy the evolution of the Galactic disk. The aim of this work is to study the kinematical behavior of the OC population over time. We take advantage of the latest age determinations of OCs to investigate the correlations of the 6D phase space coordinates and orbital properties with age. We also investigate the rotation curve of the Milky Way traced by OCs and we compare it to that of other observational or theoretical studies. We gathered nearly 30000 Radial Velocity (RV) measurements of OC members from both Gaia-RVS data and ground based surveys and catalogues. We computed the weighted mean RV, Galactic velocities and orbital parameters of 1382 OCs. We investigated their distributions as a function of age, and by comparison to field stars. We provide the largest RV catalogue available for OCs, half of it based on at least 3 members. Compared to field stars, we note that OCs are not exactly on the same arches in the radial-azimuthal velocity plane, while they seem to follow the same diagonal ridges in the Galactic radial distribution of azimuthal velocities. Velocity ellipsoids in different age bins all show a clear anisotropy. The heating rate of the OC population is similar to that of field stars for the radial and azimuthal components but significantly lower for the vertical component. The rotation curve drawn by our sample of clusters shows several dips, which match the wiggles derived from non-axisymmetric models of the Galaxy. From the computation of orbits, we obtain a clear dependence of the maximum height and eccentricity with age. Finally, the orbital characteristics of the sample of clusters as shown by the action variables, follow the distribution of field stars. The additional age information of the clusters points towards some (weak) age dependence of the known moving groups., Comment: Accepted for publication in A&A, 16 pages, 14 figures

The study of open-cluster chemical abundances provides insights on stellar nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V, Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This represents a homogeneous sample regarding the instrument features, method, line list and solar abundances from confirmed member stars. We perform an extensive comparison with previous results in the literature, and in particular with the Gaia FGK Benchmark stars Arcturus and $\mu$Leo. We investigate the dependence of [X/Fe] with metallicity, Galactocentric radius ($6.5

Context: NGC 2682 is a nearby open cluster, approximately 3.5 Gyr old. Dynamically, most open clusters should dissolve on shorter timescales, of ~ 1 Gyr. Having survived until now, NGC 2682 was likely much more massive in the past, and is bound to have an interesting dynamical history. Aims: We investigate the spatial distribution of NGC 2682 stars to constrain its dynamical evolution, especially focusing on the marginally bound stars in the cluster outskirts. Methods: We use Gaia DR2 data to identify NGC 2682 members up to a distance of ~150 pc (10 degrees). Two methods (Clusterix and UPMASK) are applied to this end. We estimate distances to obtain three-dimensional stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters. We calculate the orbit of NGC 2682 using the GRAVPOT16 software. Results: The cluster extends up to 200 arcmin (50 pc) which implies that its size is at least twice as previously believed. This exceeds the cluster Hill sphere based on the Galactic potential at the distance of NGC 2682. Conclusions: The extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation. The former origin is plausible given the orbit of NGC 2682, which crossed the Galactic disk ~40 Myr ago., Comment: 9 pages, 5 figures, accepted for publication on A&A

Context: Open clusters are ideal laboratories to investigate a variety of astrophysical topics, from the properties of the Galactic disk to stellar evolutionary models. Knowing their metallicity and possibly detailed chemical abundances is therefore important. However, the number of systems with chemical abundances determined from high resolution spectroscopy is still small.\\ Aims: To increase the number of open clusters with radial velocities and chemical abundances determined from high resolution spectroscopy we used publicly available catalogues of surveys in combination with Gaia data.\\ Methods: Open cluster stars have been identified in the APOGEE and GALAH spectroscopic surveys by cross-matching their latest data releases with stars for which high-probability astrometric membership has been derived in many clusters on the basis of the Gaia second data release.\\ Results: Radial velocities have been determined for 131 and 14 clusters from APOGEE and GALAH data, respectively. This is the first radial velocity determination from high resolution spectra for 16 systems. Iron abundances have been obtained for 90 and 14 systems from APOGEE and GALAH samples, respectively. To our knowledge 66 of these clusters (57 in APOGEE and 9 in GALAH) do not have previous determinations in the literature. For 90 and 7 clusters in the APOGEE and GALAH samples, respectively, we have also determined average abundances for Na, Mg, Al, Si, Ca, Cr, Mn, and Ni., Comment: 20 pages, accepte for publication in Astronomy & Astrophysics

$Context$. Gaia Second Data Release provides precise astrometry and photometry for more than 1.3 billion sources. This catalog opens a new era concerning the characterization of open clusters and test stellar models, paving the way for a better understanding of the disc properties. $Aims$. The aim of the paper is to improve the knowledge of cluster parameters, using only the unprecedented quality of the Gaia photometry and astrometry. $Methods$. We make use of the membership determination based on the precise Gaia astrometry and photometry. We apply anautomated Bayesian tool, BASE-9, to fit stellar isochrones on the observed G, GBP, GRP magnitudes of the high probability member stars. $Results$. We derive parameters such as age, distance modulus and extinction for a sample of 269 open clusters, selecting only low reddening objects and discarding very young clusters, for which techniques other than isochrone-fitting are more suitable for estimating ages., Comment: 14 pages, 11 figures. Submitted

Context. Open clusters are very good tracers of the evolution of the Galactic disc. Thanks to Gaia, their kinematics can be investigated with an unprecedented precision and accuracy. Aims. The distribution of open clusters in the 6D phase space is revisited with Gaia DR2. Methods. The weighted mean radial velocity of open clusters was determined, using the most probable members available from a previous astrometric investigation that also provided mean parallaxes and proper motions. Those parameters, all derived from Gaia DR2 only, were combined to provide the 6D phase space information of 861 clusters. The velocity distribution of nearby clusters was investigated, as well as the spatial and velocity distributions of the whole sample as a function of age. A high quality subsample was used to investigate some possible pairs and groups of clusters sharing the same Galactic position and velocity. Results. For the high quality sample that has 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km/s. The accuracy, assessed by comparison to ground-based high resolution spectroscopy, is better than 1 km/s. Open clusters nicely follow the velocity distribution of field stars in the close Solar neighbourhood previously revealed by Gaia DR2. As expected, the vertical distribution of young clusters is very flat but the novelty is the high precision to which this can be seen. The dispersion of vertical velocities of young clusters is at the level of 5 km/s. Clusters older than 1 Gyr span distances to the Galactic plane up to 1 kpc with a vertical velocity dispersion of 14 km/s, typical of the thin disc. Five pairs of clusters and one group with five members are possibly physically related. Other binary candidates previously identified turn out to be chance alignment., Comment: Tables 4 and 5, and Fig. 12 of Sect. 3.3 corrected in the corrigendum sent to A&A

IC 166 is an intermediate-age open cluster ($\sim 1$ Gyr) which lies in the transition zone of the metallicity gradient in the outer disc. Its location, combined with our very limited knowledge of its salient features, make it an interesting object of study. We present the first high-resolution spectroscopic and precise kinematical analysis of IC 166, which lies in the outer disc with $R_{GC} \sim 12.7$ kpc. High resolution \textit{H}-band spectra were analyzed using observations from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We made use of the Brussels Automatic Stellar Parameter (BACCHUS) code to provide chemical abundances based on a line-by-line approach for up to eight chemical elements (Mg, Si, Ca, Ti, Al, K, Mn and Fe). The $\alpha-$element (Mg, Si, Ca and whenever available Ti) abundances, and their trends with Fe abundances have been analysed for a total of 13 high-likelihood cluster members. No significant abundance scatter was found in any of the chemical species studied. Combining the positional, heliocentric distance, and kinematic information we derive, for the first time, the probable orbit of IC 166 within a Galactic model including a rotating boxy bar, and found that it is likely that IC 166 formed in the Galactic disc, supporting its nature as an unremarkable Galactic open cluster with an orbit bound to the Galactic plane., Comment: 16 pages, 7 tables, 8 figures, accepted for publication in AJ

Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the sub-milliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. In this study we aim to a establish list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. We compile a list of thousands of known or putative clusters from the literature. We then apply an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of GaiaDR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study., Comment: Accepted A&A, 19 pages, 13+20 figures, full data will be available at CDS

A wealth of tiny galaxies populates the surroundings of the Milky Way. Some of these objects might have their origin as former satellites of the Large Magellanic Cloud. Examples of the importance of understanding how many systems are genuine satellites of the MW or the LMC are the implications that the number and mass function of satellites have for dark matter theories and the treatment of baryonic physics in simulations of structure formation. Here we aim at deriving the bulk motions and estimates of the internal velocity dispersion and metallicity properties in four recently discovered distant southern dwarf galaxy candidates, Columba I, Reticulum III, Phoenix II and Horologium II. We combine Gaia DR2 astrometric measurements, photometry and new FLAMES spectroscopic data in the region of the CaII triplet lines; such combination is essential for finding potential member stars in these low luminosity systems. We find very likely member stars in all four satellites and are able to determine (or place limits on) the systems bulk motions and average internal properties. The systems are found to be very metal-poor, in agreement with dwarf galaxies and dwarf galaxy candidates of similar luminosity. The only system that we can place firmly in the category of dwarf galaxies is Phx II, given its resolved large velocity dispersion ($9.5_{-4.4}^{+6.8}$ km/s) and intrinsic metallicity spread (0.33 dex). Also for Col I we measure a clear metallicity spread. The orbital pole of Phx II is well constrained and close to that of the LMC, suggesting a prior association. The uncertainty on the orbital poles of the other systems are presently very large, so that an association cannot be excluded, apart from Col I. Using the numbers of potential former satellites of the LMC identified here and in the literature, we obtain for the LMC a dark matter mass of M$_{200}=1.9_{-0.9}^{+1.3}\times10^{11}$ M$_\odot$., Comment: 16 pages, 11 figures, 4 tables, accepted for publication in A&A

We present elemental abundance analysis of high-resolution spectra for five giant stars, deriving Fe, Mg, Al, C, N, O, Si and Ce abundances, and spatially located within the innermost regions of the bulge globular cluster NGC 6522, based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. } In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea of the NGC 6522 stars being formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary intra-cluster medium polluters. The peculiar abundance signature of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522., Comment: 13 pages, 8 figures, 4 tables, matches the accepted version in A&A

The stellar [$\alpha$/Fe] abundance is sometimes used as a proxy for stellar age, following standard chemical evolution models for the Galaxy, as seen by different observational results. In this work we show that the Open Cluster NGC6705/M11 has a significant $\alpha$-enhancement [$\alpha$/Fe]$>0.1$ dex, despite its young age ($\sim$300 Myr), challenging the current paradigm. We use high resolution (R$>65,000$) high signal-to-noise ($\sim$70) spectra of 8 Red Clump stars, acquired within the OCCASO survey. We determine very accurate chemical abundances of several $\alpha$ elements, using an equivalent width methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain [Si/Fe]=$0.13\pm0.05$, [Mg/Fe]=$0.14\pm0.07$, [O/Fe]=$0.17\pm0.07$, [Ca/Fe]=$0.06\pm0.05$ and [Ti/Fe]=$0.03\pm0.03$. Our results place these cluster within the group of young [$\alpha$/Fe]-enhanced field stars recently found by several authors in the literature. The ages of our stars have an uncertainty of around 50 Myr, much more precise than for field stars. By integrating the cluster's orbit in several non-axisymmetric Galactic potentials, we establish the M11's most likely birth radius to lie between 6.8-7.5 kpc from the Galactic center, not far from its current position. With the robust Open Cluster age scale, our results prove that a moderate [$\alpha$/Fe]-enhancement is no guarantee for a star to be old, and that not all $\alpha$-enhanced stars can be explained with an evolved blue straggler scenario. Based on our orbit calculations, we further argue against a Galactic bar origin of M11., Comment: 10 pages, 6 figures, accepted in A&A

We report the peculiar chemical abundance patterns of eleven atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low-Mg abundances ([Mg/Fe]$<$0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H]$\gtrsim - 1.0$) sample stars, which is at odds with actual observations of SG stars in Galactic CGs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy; a fundamental step forward to understand the Galactic formation and evolution., Comment: Accepted for publication in ApJ Letters, 11 pages, 2 Figures, 2 Tables

We analyse the poorly-studied open cluster King~1 in the second Galactic quadrant. From wide-field photometry we have studied the spatial distribution of this cluster. We determined that the centre of King~1 is located at $\alpha_{2000}=00^{\rm h}22^{\rm m}$ and $\delta_{2000}=+64\degr23\arcmin$. By parameterizing the stellar density with a King profile we have obtained a central density of $\rho_{0}=6.5\pm0.2$ star arcmin$^{-2}$ and a core radius of $r_{\rm core}=1\farcm9\pm0\farcm2$. By comparing the observed color-magnitude diagram of King~1 with those of similar open clusters and with different sets of isochrones, we have estimated an age of $2.8\pm0.3$ Gyr, a distance modulus of $(m-M)_{\rm o}=10.6\pm0.1$ mag, and a reddening of $E(B-V)=0.80\pm0.05$ mag. To complete our analysis we acquired medium resolution spectra for 189 stars in the area of King~1. From their derived radial velocities we determined an average velocity $\left\langle V_r\right\rangle $=-53.1$\pm$3.1 km s$^{-1}$. From the strength of the infrared \mbox{Ca\,{\sc ii}} lines in red giants we have determined an average metallicity of $\left\langle [M/H]\right\rangle$=+0.07$\pm$0.08 dex. From spectral synthesis we have also estimated an $\alpha$-elements abundance of $\left\langle [\alpha/M]\right\rangle$=-0.10$\pm$0.08 dex., Comment: 14 pages, 18 figures, table 1 will be available at CDS, Accepted for publication at MNRAS

Open Clusters have long been used to study the chemo-dynamical evolution of the Galactic disk. This requires an homogeneously analysed sample covering a wide range of ages and distances. In this aper we present the OCCASO second data release. This comprises a sample of high-resolution ($R>65,000$) and high signal-to-noise spectra of 115 Red Clump stars in 18 Open Clusters. We derive atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, $\xi$), and [Fe/H] abundances using two analysis techniques: equivalent widths and spectral synthesis. A detailed comparison and a critical review of the results of the two methods are made. Both methods are carefully tested between them, with the \emph{Gaia} FGK Benchmark stars, and with an extensive sample of literature values. We perform a membership study using radial velocities and the resulting abundances. Finally, we compare our results with a chemo-dynamical model of the Milky Way thin disk concluding that the oldest Open Clusters are consistent with the models only when dynamical effects are taken into account., Comment: 19 pages, 11 figures MNRAS accepted for publication

Baade's window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Due to its low and homogeneous interstellar absorption it is considered as a calibration field for Galactic bulge studies. In the era of large spectroscopic surveys, calibration fields such as BW are necessary to cross calibrate the stellar parameters and individual abundances of the APOGEE survey. We use the APOGEE BW stars to derive their metallicity distribution function (MDF) and individual abundances, for $\alpha$- and iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age distribution for stars in BW. We determine the MDF of APOGEE stars in BW and find a remarkable agreement with that of the Gaia-ESO survey (GES). Both exhibit a clear bimodal distribution. We also find that the Mg-metallicity planes of both surveys agree well, except for the metal-rich part ([Fe/H] >0.1), where APOGEE finds systematically higher Mg abundances with respect to the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution, with a major old population at 10 Gyr, with a decreasing tail towards younger stars. A comparison between APOGEE estimates and stellar parameters, and those determined by other sources reveals detectable systematic offsets, in particular for spectroscopic surface gravity estimates. In general, we find a good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni from APOGEE with that of literature values. We have shown that in general APOGEE data show a good agreement in terms of MDF and individual chemical abundances with respect to literature works. Using the [C/N] ration we found a significant fraction of young stars in BW which is in agreement with the model of Haywood et al. (2016)., Comment: 14 pages, 15 figure, accepted for Astronomy&Astrophysics

The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Only two dozen stars with ([Fe/H]< -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey, and followed-up with medium resolution spectroscopy on the 4.2 m William Herschel Telescope and, in a few cases, at high resolution on the the 9.2 m Hobby-Eberly Telescope. Stellar parameters and the abundances of magnesium, calcium, iron, and strontium have been inferred from the spectra using classical model atmospheres. We have also derived carbon abundances from the G band. We find consistency between the metallicities estimated from SDSS and those from new data at the level of 0.3 dex. The analysis of medium resolution data obtained with ISIS on the WHT allow us to refine the metallicities and in some cases measure other elemental abundances. Our sample contains 11 new metal-poor stars with [Fe/H] < -3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We also discuss metallicity discrepancies of some stars in common with previous works in the literature. Only one of these stars is found to be C-enhanced at about [C/Fe]~+1, whereas the other metal-poor stars show C abundances at the level of [C/Fe]~+0.45., Comment: Accepted for publication in A&A

We report on detection, from observations obtained with the APOGEE spectroscopic survey, of a metal-poor ([Fe/H] $= -1.3$ dex) field giant star with an extreme Mg-Al abundance ratio ([Mg/Fe] $= -0.31$ dex; [Al/Fe] $= 1.49$ dex). Such low Mg/Al ratios are seen only among the second-generation population of globular clusters, and are not present among Galactic disk field stars. The light element abundances of this star, 2M16011638-1201525, suggest that it could have been born in a globular cluster. We explore several origin scenarios, in particular studying the orbit of the star to check the probability of it being kinematically related to known globular clusters. We performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 globular clusters, looking for close encounters in the past with a minimum distance approach within the tidal radius of each cluster. We found a very low probability that 2M16011638-1201525 was ejected from most globular clusters; however, we note that the best progenitor candidate to host this star is globular cluster $\omega$ Centauri (NGC 5139). Our dynamical investigation demonstrates that 2M16011638-1201525 reaches a distance $|Z_{max}| < 3 $ kpc from the Galactic plane and a minimum and maximum approach to the Galactic center of $R_{min}<0.62$ kpc and $R_{max}<7.26$ kpc in an eccentric ($e\sim0.53$) and retrograde orbit. Since the extreme chemical anomaly of 2M16011638-1201525 has also been observed in halo field stars, this object could also be considered a halo contaminant, likely been ejected into the Milky Way disk from the halo. We conclude that, 2M16011638-20152 is also kinematically consistent with the disk but chemically consistent with halo field stars., Comment: Accepted for publication in ApJ

We examine the distribution of the [O/Fe] abundance ratio in stars across the Galactic disk using H-band spectra from the Apache Point Galactic Evolution Experiment (APOGEE). We minimize systematic errors by considering groups of stars with similar atmospheric parameters. The APOGEE measurements in the Sloan Digital Sky Survey Data Release 12 reveal that the square root of the star-to-star cosmic variance in the oxygen-to-iron ratio at a given metallicity is about 0.03-0.04 dex in both the thin and thick disk. This is about twice as high as the spread found for solar twins in the immediate solar neighborhood and the difference is probably associated to the wider range of galactocentric distances spanned by APOGEE stars. We quantify the uncertainties by examining the spread among stars with the same parameters in clusters; these errors are a function of effective temperature and metallicity, ranging between 0.005 dex at 4000 K and solar metallicity, to about 0.03 dex at 4500 K and [Fe/H]= -0.6. We argue that measuring the spread in [O/Fe] and other abundance ratios provides strong constraints for models of Galactic chemical evolution., Comment: 6 pages, 4 figures; A&A, accepted

Open clusters (OCs) are crucial for studying the formation and evolution of the Galactic disc. However, the lack of a large number of OCs analyzed homogeneously hampers the investigations about chemical patterns and the existence of Galactocentric radial and vertical gradients, or an age-metallicity relation. To overcome this, we have designed the Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO). We aim to provide homogeneous radial velocities, physical parameters and individual chemical abundances of six or more Red Clump stars for a sample of 25 old and intermediate-age OCs visible from the Northern hemisphere. To do so, we use high resolution spectroscopic facilities (R> 62,000) available at Spanish observatories. We present the motivation, design and current status of the survey, together with the first data release of radial velocities for 77 stars in 12 OCs, which represents about 50% of the survey. We include clusters never studied with high-resolution spectroscopy before (NGC~1907, NGC~6991, NGC~7762), and clusters in common with other large spectroscopic surveys like the Gaia-ESO Survey (NGC~6705) and APOGEE (NGC~2682 and NGC~6819). We perform internal comparisons between instruments to evaluate and correct internal systematics of the results, and compare our radial velocities with previous determinations in the literature, when available. Finally, radial velocities for each cluster are used to perform a preliminar kinematic study in relation with the Galactic disc., Comment: 20 pages, 9 figures

Context: Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature. Aims: We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters. Methods: We acquired medium-resolution spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5~m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain). Radial velocities were obtained by cross-correlation fitting techniques. The relationships available in the literature between the strength of infrared Ca II lines and metallicity were also used to derive the metallicity for each cluster. Results: We obtain = 48.6+/-3.4, -58.4+/-6.8, 26.0+/-4.3 and -65.3+/-3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603 and NGC 7245, respectively. We found [Fe/H] =-0.25+/-0.14 and -0.15+/-0.18 for NGC 559 and NGC 7245, respectively. Berkeley 23 has a low metallicity, [Fe/H] =-0.42+/-0.13, similar to other open clusters in the outskirts of the Galactic disc. In contrast, we derived a high metallicity ([Fe/H] =+0.43+/-0.15) for NGC 6603, which places this system among the most metal rich known open clusters. To our knowledge, this is the first determination of radial velocities and metallicities from spectroscopy for these clusters, except NGC 6603, for which radial velocities had been previously determined. We have also analysed ten stars in the line of sight to King 1. Because of the large dispersion obtained in both radial velocity and metallicity, we cannot be sure that we have sampled true cluster members., Comment: 10 pages, 5 figures, accepted for publication in A&A (minor modifications)

The Sloan Digital Sky Survey--III (SDSS--III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high resolution (R $\sim$ 22,500), high signal-to-noise ratio ($>$ 100) spectra in the H$-$band ($\sim$1.5$-$1.7 $\mu$m) for about 146,000 stars in the Milky Way galaxy. We have computed spectral libraries with effective temperature ($T\rm{_{eff}}$) ranging from 3500 to 8000 K for the automated chemical analy\-sis of the survey data. The libraries, used to derive stellar parameters and abundances from the APOGEE spectra in the SDSS--III data release 12 (DR12), are based on ATLAS9 model atmospheres and the ASS$\epsilon$T spectral synthesis code. We present a second set of libraries based on MARCS model atmospheres and the spectral synthesis code Turbospectrum. The ATLAS9/ASS$\epsilon$T ($T\rm{_{eff}}$ = 3500$-$8000 K) and MARCS/Turbospectrum ($T\rm{_{eff}}$ = 3500$-$5500 K) grids cover a wide range of metallicity ($-$2.5 $\leq$ [M/H] $\leq$ $+$0.5 dex), surface gravity (0 $\leq$ log $g$ $\leq$ 5 dex), microturbulence (0.5 $\leq$ $\xi$ $\leq$ 8 km~s$^{-1}$), carbon ($-$1 $\leq$ [C/M] $\leq$ $+$1 dex), nitrogen ($-$1 $\leq$ [N/M] $\leq$ $+$1 dex), and $\alpha$-element ($-$1 $\leq$ [$\alpha$/M] $\leq$ $+$1 dex) variations, having thus seven dimensions. We compare the ATLAS9/ASS$\epsilon$T and MARCS/Turbospectrum libraries and apply both of them to the analysis of the observed H$-$band spectra of the Sun and the K2 giant Arcturus, as well as to a selected sample of well-known giant stars observed at very high-resolution. The new APOGEE libraries are publicly available and can be employed for chemical studies in the H$-$band using other high-resolution spectrographs., Comment: 45 pages, 11 figures; accepted for publication in the Astronomical Journal

We present the motivation, design and current status of the Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO). Using the high resolution spectroscopic facilities available at Spanish observatories, OCCASO will derive chemical abundances in a sample of 20 to 25 open clusters older than 0.5 Gyr. This sample will be used to study in detail the formation and evolution of the Galactic disc using open clusters as tracers., Comment: 6 pages, 1 figure, Highlights of Spanish Astrophysics VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical Society held on September 8 - 12, 2014, in Teruel, Spain. A. J. Cenarro, F. Figueras, C. Hern\'andez-Monteagudo, J. Trujillo, and L. Valdivielso (eds.)

As part of a long term programme, we analyse the evolutionary status and properties of the old and populous open cluster Trumpler 5 (Tr 5), located in the Galactic anticentre direction, almost on the Galactic plane. Tr 5 was observed with WFI@MPG/ESO Telescope using the Bessel $U$, $B$, and $V$ filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMD with a library of synthetic CMDs generated with different stellar evolution sets (Padova, FRANEC, and FST). Age, reddening, and distance are derived through the synthetic CMD method using stellar evolutionary models with subsolar metallicity ($Z=0.004$ or $Z=0.006$). Additional spectroscopic observations with UVES@VLT of three red clump stars of the cluster were used to determine more robustly the chemical properties of the cluster. Our analysis shows that Tr 5 has subsolar metallicity, with [Fe/H]$=-0.403\pm0.006$ dex (derived from spectroscopy), age between 2.9 and 4 Gyr (the lower age is found using stellar models without core overshooting), reddening $E(B-V)$ in the range 0.60 to 0.66 mag complicated by a differential pattern (of the order of $\sim\pm0.1$ mag), and distance modulus $(m-M)_0=12.4\pm0.1$ mag., Comment: Paper Accepted for publication in MNRAS

We study the evolution of three fields in the outer LMC disk Rgc=3.5-6.2 Kpc. Their star formation history indicates a stellar populations gradient such that younger stellar populations are more centrally concentrated. We identify two main star forming epochs, separated by a period of lower activity between ~7 and ~4 Gyr ago. Their relative importance varies from a similar amount of stars formed in the two epochs in the innermost field, to only 40% of the stars formed in the more recent epoch in the outermost field. The young star forming epoch continues to the present time in the innermost field, but lasted only till ~0.8 and 1.3 Gyr ago at Rgc=5.5 degrees and 7.1 degrees, respectively. This gradient is correlated with the measured HI column density and implies an outside-in quenching of the star formation, possibly related to a variation of the size of the HI disk. This could either result from gas depletion due to star formation or ram-pressure stripping, or from to the compression of the gas disk as ram-pressure from the Milky Way halo acted on the LMC interstellar medium. The latter two situations may have occurred when the LMC first approached the Milky Way., Comment: 15 pages, 13 figures, 4 tables. MNRAS, in press