# Posts Tagged galactic disk

## Recent Postings from galactic disk

### Widespread Rotationally-Hot Hydronium Ion in the Galactic Interstellar Medium

We present new observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ~ 500 K, rotational temperatures characterizing the population of the highly-excited metastable H3O+ rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone, but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ~ 380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic ray fluxes, shocks and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly-excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation to the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process, not limited to the active environments associated with galactic nuclei.

### The Galactic bar and the large scale velocity gradients in the Galactic disk

We investigate whether the cylindrical (galactocentric) radial velocity gradient of ~ -3 km/sec/kpc, directed radially from the Galactic center and recently observed in the stars of the Solar Neighborhood with the RAVE survey, can be explained by the resonant effects of the bar near the Solar Neighborhood. We compare the results of test particle simulations of the Milky Way with a potential including a rotating bar with observations from the RAVE survey. To this end we apply the RAVE selection function to the simulations, and convolve these with the characteristic RAVE errors. We explore different "solar neighborhoods" in the simulations as well as different bar models. We find that the bar induces a negative radial velocity gradient at every height from the Galactic plane, outside the Outer Lindblad Resonance, and for angles from the long axis of the bar compatible with the current estimates. The selection function and errors do not wash away the gradient, but often make it steeper, especially near the Galactic plane because this is where the RAVE survey is less radially extended. No gradient in the vertical velocity is present in our simulations, from which we may conclude that this cannot be induced by the bar.

### The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk

We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters (including non-LTE), and the survey selection effects, which are caused by observing the stars in a given photometric box. We find that the colour and magnitude cuts on the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as large as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages (0.5 to 13.5 Gyr), Galacto-centric distances from $6$ to 9.5 kpc and vertical distances above the plane 0 < |Z| < 1.5 kpc.In the context of Galaxy formation, we find that: i) the observed age-metallicity relation is nearly flat in the range of ages between 0 and 8 Gyr, ii) there is a decline in [Fe/H] for stars with ages above 9 Gyr, which is where we detect no metal-rich stars at all; this cannot be explained by the survey selection functions, iii) there is a significant scatter of [Fe/H] at any age. In agreement with earlier work in the literature, we find that radial abundance gradients change as a function of vertical distance above the plane. The Mg gradient steepens and becomes negative. There is a well-defined double-branching of Mg abundances for stars at |Z| > 300 pc above the plane: the low and high alpha-components partly overlapping in age. The dispersion of [Mg/Fe] abundances is significant at any age. In particular, the stars with ages above 9 Gyr show a broad range in both [Mg/Fe], from 0 to 0.4 dex, and metallicity, from solar to [Fe/H] ~ -1.

### The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705

Open clusters are key tools to study the spatial distribution of abundances in the disk and their evolution with time. Using the first release of stellar parameters and abundances of the Gaia-ESO Survey, we analyse the chemical properties of stars in three old/intermediate-age open clusters, namely NGC 6705, NGC 4815, and Trumpler 20, all located in the inner part of the Galactic disk at Galactocentric radius R$_{GC}\sim$7 kpc, aiming at proving their homogeneity and at comparing them with the field population. We study the abundance ratios of elements belonging to two different nucleosynthetic channels: $\alpha$-elements and iron-peak elements. The main results can be summarised as follows: i) cluster members are chemically homogeneous within 3-$\sigma$ in all analysed elements; ii) the three clusters have comparable [El/Fe] patters within $\sim$1-$\sigma$, but they differ in their global metal content [El/H], with NGC 4815 having the lowest metallicity. Their [El/Fe] ratios show differences and analogies with those of the field population, both in the solar neighbourhood and in the bulge/inner disk; iii) comparing the abundance ratios with the results of two chemical evolution models and with field star abundance distributions, we find that the abundance ratios of Mg, Ni, Ca in NGC 6705 might require an inner birthplace, implying a subsequent variation of its R$_{GC}$ during its lifetime, consistent with previous orbit determination. The full dataset of the Gaia-ESO Survey will be a superlative tool to constrain the chemical evolution of our Galaxy by disentangling different formation and evolution scenarios.

### The WISE Catalog of Galactic HII Regions

Using data from the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite, we made a catalog of over 8000 Galactic HII regions and HII region candidates by searching for their characteristic mid-infrared (MIR) morphology. WISE has sufficient sensitivity to detect the MIR emission from HII regions located anywhere in the Galactic disk. We believe this is the most complete catalog yet of regions forming massive stars in the Milky Way. Of the ~8000 cataloged sources, ~1500 have measured radio recombination line (RRL) or H$\alpha$ emission, and are thus known to be HII regions. This sample improves on previous efforts by resolving HII region complexes into multiple sources and by removing duplicate entries. There are ~2500 candidate HII regions in the catalog that are spatially coincident with radio continuum emission. Our group’s previous RRL studies show that ~95% of such targets are HII regions. We find that ~500 of these candidates are also positionally associated with known HII region complexes, so the probability of their being bona fide HII regions is even higher. At the sensitivity limits of existing surveys, ~4000 catalog sources show no radio continuum emission. Using data from the literature, we find distances for ~1500 catalog sources, and molecular velocities for ~1500 HII region candidates.

### On the alignment of PNe and local magnetic field at the galactic centre: MHD numerical simulations

For the past decade observations of the alignement of PNe symmetries with respect to the galactic disk have led to conflicting results. Recently observational evidence for alignment between PNe and local interstellar magnetic fields in the central part of the Galaxy ($b < 5^\circ$) has been found. We studied the role of the interstellar magnetic field on the dynamical evolution of a PN by means of an analytical model and from 3D MHD numerical simulations. We test under what conditions typical ejecta would have their dynamics severely modified by an interstellar magnetic field. We found that uniform fields of $> 100\mu$G are required in order to be dynamically dominant. This is found to occur only at later evolutionary stages, therefore being unable to change the general morphology of the nebula. However, the symmetry axis of bipolar and elliptical nebulae end up aligned to the external field. This result can explain why different samples of PNe result in different conclusions regarding the alignment of PNe. Objects located at high galactic latitudes, or at large radii, should present no preferential alignment with respect to the galactic plane. PNe located at the galactic centre and low latitudes would, on the other hand, be preferentiably aligned to the disk. Finally, we present synthetic polarization maps of the nebulae to show that the polarization vectors, as well as the field lines at the expanding shell, are not uniform even in the strongly magnetized case, indicating that polarization maps of nebulae are not adequate in probing the orientation, or intensity, of the dominant external field.

### Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields [Replacement]

We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31 Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating white dwarf, and 58 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. Our sample also includes candidates for Type II Cepheids and unclassified short-period (P<0.23 d) multi-mode stars which could be either delta Sct or beta Cep type stars. One of the detected variables is a very likely delta Sct star with an exceptionally high peak-to-peak I-band amplitude of 0.35 mag at the very short period of 0.0196 d. All reported pulsating variables but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers more than half of the Galactic plane. For the purposes of future works on the spiral structure and star formation history of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.

### Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields

We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 14 Long-Period Variables, such as Miras and Semi-Regular Variables, and 56 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. All reported pulsating variables but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers half of the Galactic plane. For the purposes of future works on the spiral structure and star formation history of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.

### Analyzing spiral structure in a galactic disk with a gaseous component

Using GADGET2, we performed an SPH+N-body simulation of a galactic disk with stellar and gas particles. This simulation allows to compare the spiral structure in the different disk components. Also, we performed a simulation without gaseous component to explore the effects of the gas in the spiral pattern of the stars.

### Thermals in stratified regions of the ISM

We present a model of a "thermal" (i.e., a hot bubble) rising within an exponentially stratified region of the ISM. This model includes terms representing the ram pressure braking and the entrainment of environmental gas into the thermal. We then calibrate the free parameters associated with these two terms through a comparison with 3D numerical simulations of a rising bubble. Finally, we apply our "thermal" model to the case of a hot bubble produced by a SN within the stratified ISM of the Galactic disk.

### A couple of recent developments in the structure of the outer disk of the Milky Way

In this contribution we summarize recent achievements by our group on the understanding of the structure of the outer Galactic disk, with particular emphasis to the outer disk extent, and the spiral structure beyond the solar circle.

### Extreme Galaxies During Reionization: Testing ISM and Disk Models

We test the ability of equilibrium galactic disk and one-zone interstellar medium models to describe the physical and emission properties of a sample of quasar hosts, submillimeter galaxies, and Lyman-alpha emitters during the epoch of cosmic reionization at z>~6. We find that the size, line widths, star formation rates, black hole accretion rates, gas masses and temperatures, and the relationships between these properties are all well-described by our model. In particular, the quasars in our sample are hosted by halos with masses of roughly 10^12–10^13 M_sun and require an inflow velocity of gas toward the disk center of v_in=sqrt(2) beta sigma with beta~0.1—somewhat higher if quasar outflows are significant—where sigma is the halo velocity dispersion. We also provide approximate fitting formulae to our results for comparison with future observations. However, our fiducial model underestimates the [CII] line emission from the systems in our sample by an order of magnitude or more. We explore two variants to our model and find that the requisite flux can be produced if either the star formation efficiency of molecular clouds is higher or the depletion of metals onto dust at fixed metallicity is lower at higher redshift than expected from standard models. Our models also predict a higher median density in molecular clouds than found in fits to observations resulting from turbulent fragmentation in molecular clouds leading to a more thermalized CO(6-5) line and a higher CO(6-5)/CO(1-0) ratio than determined observationally. While we leave this last issue unresolved in detail, we suggest that either clouds smaller than the local Jeans mass or a support mechanism other than turbulence could result in a lower turbulent Mach number and more subthermal CO(6-5) emission.

### Star Formation Sites toward the Galactic Center Region: The Correlation of CH3OH Masers, H2O Masers, and Near-IR Green Sources

We present a study of star formation in the Central Molecular Zone (CMZ) of our Galaxy through the association of three star formation indicators: 6.7 GHz CH3OH masers, 22 GHz H2O masers, and enhanced 4.5 micron emission (green’) sources. We explore how star formation in the Galactic center (l < 1.3 deg, |b| < 10′, where l and b are Galactic longitude and Galactic latitude) compares with that of the Galactic disk (6 deg < l < 345 deg, |b| < 2 deg). Using an automated algorithm, we search for enhanced 4.5 micron emission sources toward 6.7 GHz CH3OH masers detected in the Parkes Methanol Multibeam Survey. We combine these results with our 22 GHz H2O maser survey of the CMZ carried out with the Mopra telescope. We find that the correlation of CH3OH masers with green sources is a function of Galactic latitude, with a minimum close to b=0 and increasing with |b| (toward the central part of the Galaxy, 6 deg < l < 345 deg, |b| < 2 deg). We find no significant difference between the correlation rate of CH3OH masers with green sources in the CMZ and the disk. This suggests that although the physical conditions of the gas are different in the Galactic center from that of the Galactic disk, once gravitational instability sets in at sufficiently high densities, signatures of star formation appear to be similar in both regions. Moreover, the detection of green sources, even at the distance of the Galactic center, shows that our technique can easily identify the early stages of star formation, especially in low extinction regions of the Galaxy. Through the association of H2O and CH3OH masers, we identify 15 star-forming sites in the CMZ. We find no coincident H2O and CH3OH masers outside the CMZ (with limited H2O maser survey coverage outside the CMZ), possibly indicating a difference in the maser evolutionary sequence for star-forming cores in the Galactic center region and the disk.

### Substructure in bulk velocities of Milky Way disk stars

We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally. These findings are based on LAMOST spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun’s radius and +/-2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.

### Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood [Replacement]

ABRIDGED: METHODS: We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes…… The determination of stellar parameters and elemental abundances is based on a standard 1-D LTE analysis using equivalent width measurements in high-resolution (R=40000-110000) and high signal-to-noise (S/N=150-300) spectra obtained with….. RESULTS: …. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400 K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. We furthermore find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk……….. We furthermore have discovered that a standard 1-D, LTE analysis, utilising ionisation and excitation balance of Fe I and Fe II lines produces a flat lower main sequence. As the exact cause for this effect is unclear we chose to apply an empirical correction. Turn-off, and more evolved, stars, appears to be un-affected.

### Exploring the Milky Way stellar disk. A detailed elemental abundance study of 703 F and G dwarf stars in the Solar neighbourhood

AIMS: The aim of this paper is to explore and map the age and abundance structure of the stars in the nearby Galactic disk. Methods: We have conducted a high-resolution spectroscopic study of 703 F and G dwarf stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot (kinematically) be associated with either the thin disk or the thick disk. The determination of stellar parameters and elemental abundances is based on a standard 1-D LTE analysis using equivalent width measurements in high-resolution (R=40000-110000) and high signal-to-noise (S/N=150-300) spectra obtained with FEROS, SOFIN, UVES, and MIKE. NLTE corrections for individual Fe I lines were employed in every step of the analysis. Results: We present stellar parameters, stellar ages, kinematical parameters, orbital parameters, and detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 703 nearby F and G dwarf stars. Our data show there is an old and alpha-enhanced disk population, and then a younger and less alpha-enhanced disk population. While they greatly overlap in metallicity between -0.7<[Fe/H]<+0.1 they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars that are more susceptible to uncertainties and NLTE effects are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between different stellar populations are to be revealed. We furthermore find that the alpha-enhanced population have orbital parameters placing their birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, abridged…

### A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc < R < 9 kpc

We present and apply rigorous dynamical modeling with which we infer unprecedented constraints on the stellar and dark matter mass distribution within our Milky Way (MW), based on large sets of phase-space data on individual stars. Specifically, we model the dynamics of 16,269 G-type dwarfs from SEGUE, which sample 5 < R/kpc < 12 and 0.3 < |Z|/kpc < 3. We independently fit a parameterized MW potential and a three-integral, action-based distribution function (DF) to the phase-space data of 43 separate abundance-selected sub-populations (MAPs), accounting for the complex selection effects affecting the data. We robustly measure the total surface density within 1.1 kpc of the mid-plane to about 5% over the range 4.5< R/kpc < 9. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 < R/kpc < 7, while MAPs with longer radial scale lengths sample 7 < R/kpc < 9. We measure the mass-weighted Galactic disk scale length to be R_d = 2.15+/-0.14 kpc, in agreement with the photometrically inferred spatial distribution of stellar mass. We thereby measure dynamically the mass of the Galactic stellar disk to unprecedented accuracy: M_* = 4.6+/-0.3×10^{10} Msun and a total local surface density of \Sigma_{R_0}(Z=1.1 kpc) = 68+/-4 Msun/pc^2 of which 38+/-4 Msun/pc^2 is contributed by stars and stellar remnants. By combining our surface density measurements with data on the terminal velocity curve, we find that the MW’s disk is maximal in the sense that V_{c,disk} / V_{c,total} = 0.83+/-0.04 at R=2.2R_d. We also constrain for the first time the radial profile of the dark halo at such small Galactocentric radii, finding that \rho_{DM}(r) ~ 1 / r^\alpha with \alpha < 1.53 at 95% confidence. Our results show that action-based distribution-function modeling of complex stellar data sets is now a feasible approach that will be fruitful for interpreting Gaia data.

### Minimum Distance Estimation of Milky Way Model Parameters and Related Inference [Cross-Listing]

We propose a method to estimate the location of the Sun in the disk of the Milky Way using a method based on the Hellinger distance and construct confidence sets on our estimate of the unknown location using a bootstrap based method. Assuming the Galactic disk to be two-dimensional, the sought solar location then reduces to the radial distance separating the Sun from the Galactic center and the angular separation of the Galactic center to Sun line, from a pre-fixed line on the disk. On astronomical scales, the unknown solar location is equivalent to the location of us earthlings who observe the velocities of a sample of stars in the neighborhood of the Sun. This unknown location is estimated by undertaking pairwise comparisons of the estimated density of the observed set of velocities of the sampled stars, with densities estimated using synthetic stellar velocity data sets generated at chosen locations in the Milky Way disk according to four base astrophysical models. The "match" between the pair of estimated densities is parameterized by the affinity measure based on the familiar Hellinger distance. We perform a novel cross-validation procedure to establish a desirable "consistency" property of the proposed method.

### A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey

We describe the pre-OmegaTranS project, a deep survey for transiting extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we observed a single dense stellar field with a very high cadence of ~2min using the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical Wide-field System for Europe and the Munich Difference Imaging Analysis pipeline, a module that has been developed for this project, we created the light curves of 16000 stars with more than 4000 data points which we searched for periodic transit signals using a box-fitting least-squares detection algorithm. All light curves are publicly available. In the course of the pre-OmegaTranS project we identified two planet candidates – POTS-1b and POTS-C2b – which we present in this work. With extensive follow-up observations we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag the follow-up and confirmation of POTS-1b was particularly challenging and costly.

### Search for hidden turbulent gas through interstellar scintillation

Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected when the light of remote stars crosses a Galactic – disk or halo – refractive medium such as a molecular cloud. We present the promising results of a test performed with the ESO-NTT and the perspectives of detection.

### A Low Metallicity Molecular Cloud In The Lower Galactic Halo

We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21-cm emission line spectra, and FIR mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud (IVMC) that lies ~300 pc above the disk. The metallicity of IV21 was estimated using observations toward the sdB star PG1144+615, located at a projected distance of 16 pc from the cloud’s densest core, by measuring ion and HI column densities for comparison with known solar abundances. Despite the cloud’s bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log(Z/Z_Sun)=-0.43 +/- 0.12dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud’s low metallicity is also atypical for Galactic molecular clouds, especially in the light of the bright FIR emission which suggest a substantial dust content. The measured I_100mu/N(HI) ratio is a factor of three below the average found in high latitude \HI clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud (HVC) that is mixing with disk gas in the lower Galactic halo.

### Global survey of star clusters in the Milky Way II. The catalogue of basic parameters

Although they are the main constituents of the Galactic disk population, for half of the open clusters in the Milky Way reported in the literature nothing is known except the raw position and an approximate size. The main goal of this study is to determine a full set of uniform spatial, structural, kinematic, and astrophysical parameters for as many known open clusters as possible. On the basis of stellar data from PPMXL and 2MASS, we used a dedicated data-processing pipeline to determine kinematic and photometric membership probabilities for stars in a cluster region. For an input list of 3784 targets from the literature, we confirm that 3006 are real objects, the vast majority of them are open clusters, but associations and globular clusters are also present. For each confirmed object we determined the exact position of the cluster centre, the apparent size, proper motion, distance, colour excess, and age. For about 1500 clusters, these basic astrophysical parameters have been determined for the first time. For the bulk of the clusters we also derived the tidal radius. We estimated additionally average radial velocities for more than 30% of the confirmed clusters. The present sample (called MWSC) reaches both the central parts of the Milky Way and its outer regions. It is almost complete up to 1.8 kpc from the Sun and also covers neighbouring spiral arms. However, for a small subset of the oldest open clusters ($\log t \gtrsim 9$) we found some evidence of incompleteness within about 1 kpc from the Sun.

### Barium and Yttrium abundance in intermediate-age and old open clusters

Barium is a neutron capture element, that, in open clusters, is frequently over-abundant with respect to the Iron. A clear explanation for this is still missing. Additionally, its gradient across the Galactic disk is poorly constrained. We measure the abundance of yttrium and barium using the synthetic spectrum method from UVES high-resolution spectra of eight distant open clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75, NGC 6192, NGC 6404, and NGC 6583. The barium abundance was estimated using NLTE approximation. We confirm that Barium is indeed over-abundant in most clusters, especially young clusters. Finally, we investigated the trend of yttrium and barium abundances as a function of distance in the Galaxy and ages. Several scenarios for the barium over-abundance are then discussed.