Context. Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than less than or similar to 150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements. Aims. In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques. Methods. We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (tau < 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe I, Fe II, Tit, Tin,Na I, Mg I, Al I,Sit, Ca I, Cr I, and Ni I. Results. Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated. Conclusions. Our clusters display a metallicity [Fe/H] between +0.04 +/- 0.01 and +0.12 +/- 0.02; they are not more metal poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models.

We present the combination of optical data from the Science Verification phase of the Dark Energy Survey (DES) with near-infrared (NIR) data from the European Southern Observatory VISTA Hemisphere Survey (VHS). The deep optical detections from DES are used to extract fluxes and associated errors from the shallower VHS data. Joint seven-band (grizYJK) photometric catalogues are produced in a single 3 sq-deg dedicated camera field centred at 02h26m-04d36m where the availability of ancillary multiwavelength photometry and spectroscopy allows us to test the data quality. Dual photometry increases the number of DES galaxies with measured VHS fluxes by a factor of similar to 4.5 relative to a simple catalogue level matching and results in a similar to 1.5 mag increase in the 80 per cent completeness limit of the NIR data. Almost 70 per cent of DES sources have useful NIR flux measurements in this initial catalogue. Photometric redshifts are estimated for a subset of galaxies with spectroscopic redshifts and initial results, although currently limited by small number statistics, indicate that the VHS data can help reduce the photometric redshift scatter at both z < 0.5 and z > 1. We present example DES VHS colour selection criteria for high-redshift luminous red galaxies (LRGs) at z similar to 0.7 as well as luminous quasars. Using spectroscopic observations in this field we show that the additional VHS fluxes enable a cleaner selection of both populations with <10 per cent contamination from galactic stars in the case of spectroscopically confirmed quasars and <0.5 per cent contamination from galactic stars in the case of spectroscopically confirmed LRGs. The combined DES+VHS data set, which will eventually cover almost 5000 sq-deg, will therefore enable a range of new science and be ideally suited for target selection for future wide-field spectroscopic surveys.

The VLT Survey Telescope (VST) ATLAS is an optical ugriz survey aiming to cover ~4700deg^2 of the Southern sky to similar depths as the Sloan Digital Sky Survey (SDSS). From reduced images and object catalogues provided by the Cambridge Astronomical Surveys Unit we first find that the median seeing ranges from 0.8 arcsec FWHM in i to 1.0 arcsec in u, significantly better than the 1.2-1.5 arcsec seeing for SDSS. The 5 sigma magnitude limit for stellar sources is r_AB=22.7 and in all bands these limits are at least as faint as SDSS. SDSS and ATLAS are more equivalent for galaxy photometry except in the z band where ATLAS has significantly higher throughput. We have improved the original ESO magnitude zeropoints by comparing m<16 star magnitudes with APASS in gri, also extrapolating into u and z, resulting in zeropoints accurate to ~+-0.02 mag. We finally compare star and galaxy number counts in a 250deg^2 area with SDSS and other count data and find good agreement. ATLAS data products can be retrieved from the ESO Science Archive, while support for survey science analyses is provided by the OmegaCAM Science Archive (OSA), operated by the Wide-Field Astronomy Unit in Edinburgh.

Context. A key science goal of the Gaia-ESO survey (GES) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive Wolf-Rayet binary system gamma(2) Velorum was one of the first GES targets.Aims. We empirically determine the radial velocity precision of GES data, construct a kinematically unbiased sample of cluster members and characterise their dynamical state.Methods. Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy was used to derive radial velocities and assess membership from the strength of the Li I 6708 angstrom line. The radial velocity distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries.Results. The GES radial velocity precision is about 0.25 km s(-1) and sufficient to resolve velocity structure in the low-mass population around gamma(2) Vel. The structure is well fitted by two kinematic components with roughly equal numbers of stars; the first has an intrinsic dispersion of 0.34 +/- 0.16 km s(-1), consistent with virial equilibrium. The second has a broader dispersion of 1.60 +/- 0.37 km s(-1) and is offset from the first by congruent to 2 kms(-1). The first population is older by 1-2 Myr based on a greater level of Li depletion seen among its M-type stars and is probably more centrally concentrated around gamma(2) Vel.Conclusions. We consider several formation scenarios, concluding that the two kinematic components are a bound remnant of the original, denser cluster that formed gamma(2) Vel, and a dispersed population from the wider Vela OB2 association, of which gamma(2) Vel is the most massive member. The apparent youth of gamma(2) Vel compared to the older (>= 10 Myr) low-mass population surrounding it suggests a scenario in which the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars.

The Gaia-ESO Survey is a large public spectroscopic survey that aims to derive radial velocities and fundamental parameters of about 10(5) Milky Way stars in the field and in clusters. Observations are carried out with the multi-object optical spectrograph FLAMES, using simultaneously the medium-resolution (R similar to 20 000) GIRAFFE spectrograph and the high-resolution (R similar to 47 000) UVES spectrograph. In this paper we describe the methods and the software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra. Data reduction has been performed using a workflow specifically developed for this project. This workflow runs the ESO public pipeline optimizing the data reduction for the Gaia-ESO Survey, automatically performs sky subtraction, barycentric correction and normalisation, and calculates radial velocities and a first guess of the rotational velocities. The quality control is performed using the output parameters from the ESO pipeline, by a visual inspection of the spectra and by the analysis of the signal-to-noise ratio of the spectra. Using the observations of the first 18 months, specifically targets observed multiple times at different epochs, stars observed with both GIRAFFE and UVES, and observations of radial velocity standards, we estimated the precision and the accuracy of the radial velocities. The statistical error on the radial velocities is sigma similar to 0.4 km s(-1) and is mainly due to uncertainties in the zero point of the wavelength calibration. However, we found a systematic bias with respect to the GIRAFFE spectra (similar to 0.9 km s(-1)) and to the radial velocities of the standard stars (similar to 0.5 km s(-1)) retrieved from the literature. This bias will be corrected in the future data releases, when a common zero point for all the set-ups and instruments used for the survey is be established.

Studying quasars at the highest redshifts can constrain models of galaxy and black hole formation, and it also probes the intergalactic medium in the early universe. Optical surveys have to date discovered more than 60 quasars up to z 6.4, a limit set by the use of the z-band and CCD detectors. Only one z>6.4 quasar has been discovered, namely the z=7.08 quasar ULAS J1120+0641, using near-infrared imaging. Here we report the discovery of three new z>6.4 quasars in 332 square degrees of the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the number from 1 to 4. The newly discovered quasars have redshifts of z=6.60, 6.75, and 6.89. The absolute magnitudes are between -26.0 and -25.5, 0.6-1.1 mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the MgII emission line in all three objects. The quasars are powered by black holes with masses of (1-2)x10^9 M_sun. In our probed redshift range of 6.4410^9 M_sun) > 1.1x10^(-9) Mpc^(-3). The discovery of three quasars in our survey area is consistent with the z=6 quasar luminosity function when extrapolated to z 7. We do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z=6 to z=7.

We present the results of a high-redshift, z = 4.6, survey of [O?ii]??3727 emission line galaxies in the GOODS-S field. The survey uses deep near-infrared data in the NB2090 (?c = 2.095? mu m, ? ? = 0.02 mu m) and Ks (?c = 2.146? mu m, ? ? = 0.324 mu m) filters taken with the European Southern Observatory instrument, HAWK-I. The images reach an emission line flux limit (5s) of 3.16 x 10-18?erg?s-1?cm -2. At z = 4.6, the survey probes a comoving volume of similar to 6680?Mpc3. Three [O?ii] emission line candidates at z similar to 4.6 are selected using the Lyman-break criteria. Photometric redshift analysis supports the conclusion that these are genuine [O?ii] emitters, ruling out a z < 3 solution entirely for one of the candidates. In the analysis presented in this paper, two scenarios are considered: first, all three candidates are genuine [O?ii] emitters and secondly, only the most likely candidate is a genuine [O?ii] emitter. We use the line fluxes of these objects to place confidence limits on the star formation rate density (SFRD) in bright (log(L[O ii ])>42.0) [O?ii] emission line galaxies. Assuming an observed [O?ii]/Ha line ratio of 0.45 and A(Ha) = 1.0?mag, we report an SFRD of ??*(log(L[O ii ])>42.0)=0.058M yr -1 Mpc -3 in our objects. Using small number statistics, we then place a 50 per cent confidence interval on the global star formation rate of ??*(log(L[O ii ])>42.0)=0.058 +/- 0.013M yr -1 Mpc -3. By combining our results with those from low-z surveys, we compile the first homogeneous set of measurements of the SFRD in bright [O?ii] emitters from z = 0 to 4.6. From this, we conclude that there was an increase in the SFRD in the brightest [O?ii] emitters of at least a factor of 2 between z = 4.6 and 1.85.

We present the results of a deep, near-infrared, narrow-band imaging survey at a central wavelength of 1.062 mu m (FWHM = 0.01 mu m) in the GOODS-South field using the ESO VLT instrument, HAWK-I. The data are used to carry out the highest redshift search for [O ii] lambda 3727 A emission line galaxies to date. The images reach an emission line flux limit (5 Sigma) of 1.5 x 10-17 erg cm-2 s-1, additionally making the survey the deepest of its kind at high redshift. In this paper we identify a sample of [O ii] lambda 3727 A emission line objects at redshift z similar to 1.85 in a comoving volume of similar to 4100 Mpc-3. Objects are selected using an observed equivalent width (EWobs) threshold of EWobs > 50A. The sample is used to derive the space density and constrain the luminosity function of [O ii] emitters at z = 1.85. We find that the space density () of objects with observed [O ii] luminosities in the range is log() = -2.45 +/- 0.14 Mpc-3, a factor of 2 greater than the observed space density of [O ii] emitters reported at z similar to 1.4. After accounting for completeness and assuming an internal extinction correction of A(H alpha) = 1 mag (equivalent to = 1.87), we report a star formation rate density of M-circle dot yr-1 Mpc-3. We independently derive the dust extinction of the sample using 24-mu m fluxes and find a mean extinction of magnitudes (A(H alpha) = 0.52). This is significantly lower than the A(H alpha) = 1 ( = 1.86) mag value widely used in the literature. Finally, we incorporate this improved extinction correction into the star formation rate density measurement and report M-circle dot yr-1 Mpc-3.

We present u-, g-, r-, i- and z-band optical images and associated catalogues taken primarily with the Isaac Newton Telescope Wide Field Camera on the European Large Area ISO Survey (ELAIS) N1 and N2, First Look Survey and Lockman Hole fields comprising a total of 1000 h of integration time over 80 deg^2 and approximately 4.3 million objects. In this paper we outline the observations and data processing and characterize the completeness, reliability, photometric and astrometric accuracy of this data set. All images have been photometrically calibrated using the Sloan Digital Sky Survey and a uniform and homogeneous data set is composed over all the observed fields. Magnitude limits are u, g, r, i, z of 23.9, 24.5, 24.0, 23.3, 22.0 (AB, 5σ). These data have been used for optical identification of past and ongoing projects including the surveys ELAIS, Spitzer Wide-Area Infrared Extragalactic Survey, Spitzer Extragalactic Representative Volume Survey and Herschel Multi-tiered Extragalactic Survey.

The reduction of [Os-3(CO)(11)P(OMe)(3)] and subsequent ionic coupling of the reduced species with [Ru(eta(5)-C5H5) (CH3CN)] resulted in the formation of [Os-3(CO)(II)P(OMe)(3)(Ru(eta(5)-C5H5))(2)] which can be converted to spiked tetrahedral cluster, [HOs3(CO)(II)P(OMe)(3)Ru-2(eta(5)-C5H5)(C5H4)] via the intramolecular hydrogen transfer Due to the unavailability of a suitable single crystal, the PW91/SDD and LDA/SDD density functional methods were used to predict possible structures and the available spectroscopic information (IR, NMR) of [Os-3(CO)(11)P(OMe)(3)(Ru(eta(5)-C5H5)(2)] The most probable geometry found by constrained search is the isomer (a2) in which the phosphite, P(OMe)(3), occupies an axial position on one of the two osmium atoms that is edge bridged by the Ru(CO)(2)(eta(5)-C5H5) unit By using the most probably geometry, the predicted infrared frequencies and H-1, C-13 and P-31 NMR chemical shifts of the compound are in the same ramie as the experimental values For this type of complex. the LDA/SDD method is appropriate for IR predictions whereas the OPBE/IG LO-II method is appropriate for NMR predictions The activation energy and reaction enemy of the intramolecular hydrogen transfer coupled with the structural change of the transition metal framework were estimated at the PW91/SDD level to be 110 32 and -0 14 kcal/mol respectively

Reactions between the activated cluster [Os3(CO)10(NCMe)2] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os3H(CO)10}2(CO2CH2CO2)] (1), [{Os3H(CO)10}2(CO2C2H4CO2)] (2), and [{Os3H(CO)10}2(C4O4)] (3) in good yield. Cluster 3 was subsequently treated with [Co2(CO)8] and this results in the addition of a “Co2(CO)6” group giving [{Os3H(CO)10}2(C2O4){Co2(CO)6}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.

Thermolysis of [Ru3(CO)12] in cyclohexene for 24 h affords the complexes [Ru(CO)3(η4-C6H8)] (1), [Ru3H2(CO)9(μ2-η1:η2:η1-C6H8)] (2), [Ru4(CO)12(μ4-C6H8)] (3) [Ru4(CO)9(μ4-C6H8)(η6-C6H6)] (4a and 4b, two isomers) and [Ru5(CO)12(μ4-η2-C6H8)(η4-C6H8)] (5), where 1, 3, 4a and 4b have been previously characterised as products of the thermolysis of [Ru3(CO)12] with cyclohexa-1,3-diene. The molecular structures of the new clusters 2 and 5 were determined by single-crystal X-ray crystallography, showing that two conformational polymorphs of 5 exist in the solid state, differing in the orientation of the cyclohexa-1,3-diene ligand on a ruthenium vertex.

The ionic coupling reaction of the dianion [Os3(CO)9(R2C2)]2− (R=Me, Ph) with two equivalents of the monocation [Ru(η5-C5H5)(CH3CN)3]+ affords the neutral clusters [Os3Ru2(CO)9(R2C2)(η5-C5H5)2] [R=Me, 1 and R=Ph, 2] in ca. 80% yield. An X-ray crystallographic study of 1 confirms that these clusters exhibit a capped pseudo-octahedral Os3Ru2C2 core, with the alkyne bonded parallel to the hinge bond of the capped butterfly metal geometry in a μ4–η2 manner, the Ru atoms adopting the wing-tip and capping positions. Reaction of the activated cluster [Os3RuH(η5-C5H5)(CO)10(MeCN)] (3) with RCCR (R=Me, Ph) affords the related clusters [Os3RuH(CO)9(η5-C5H5)(R2C2)] (R=Me, 4 and R=Ph, 5) in ca. 35% yield. The reaction with PhCCPh also produces [Os3Ru(CO)8(η5-C5H5)(PhCCPh)(PhCC(H)Ph)] (6) in ca. 15% yield. An X-ray crystallographic study shows that this cluster has a pseudo-octahedral Os3RuC2 core, with the Ru(η5-C5H5) unit adopting the wing-tip position, the alkyne bonded in a μ4–η2 arrangement and the ethenyl ligand bridging an Os–Os edge in a μ2–η1:η2 configuration.

The clusters [H2Os4M(CO)12eta6-C6H6)] (M=Os, Ru) may be deprotonated to generate anions [Os4M(CO)12eta6-C6H6)]2- which react with [M′eta6-C6H5R) (MeCN)3]2+(M′=Os, Ru; R=H, Me) to give the bicapped tetrahedral clusters [Os4(CO)12MM′eta6-C6H5R)2]. Whereas [Os4(CO)12M2eta6-C6H6)2] (M=Os, Ru) have one Meta6-C6H6) unit in a site connected to three other metals, {3}, and one in a site connected to four other metals, {4}, [Os4(CO)12OsRueta6-C6H6)2] has the Rueta6-C6H6) unit in the {3} site irrespective of whether the Os or Ru anion is capped. Coupling of these anions with Au2dppm yields [Os4M(CO)12eta6-C6H6)(Au2dppm)] (M=Os, Ru), which have the arene ligand in the axial site of a trigonal bipyramid and the digold unit capping two faces. Reduction of [H2Os5(CO)15] with K/Ph2CO and coupling with [Rueta5-C5H5)(MeCN)3]2+yields the monoanion [Os5(CO)15Rueta5-C5H5)]− which reacts with [AuPPh3]+ generating [Os5(CO)15Rueta5-C5H5)(AuPPh3)] with the “Ru(C5H5)” unit in the terminal {3} site.

The triallylphosphine-substituted clusters [Ru3(CO)11{P(CH2CHCH2)3}], [Ru3(CO)10{P(CH2CHCH2)3}2] and [Ru3(CO)10{σ;π-CH2CHCH2P(CH2CHCH2)2}] have been prepared; reaction of [Ru3(CO)10{σ;π-CH2CHCH2P(CH2CHCH2)2}] with phosphines/phosphites leads to cleavage of the Ru–allyl π-bond and formation of [Ru3(CO)11{P(CH2CHCH2)3}(PR3)].

The reaction of [Os4(CO)9(RCCR)(η6-C6H6)] (R=Me, Ph) with Me3NO in the presence of 1,3-cyclohexadiene or 1,4-cyclohexadiene yields the clusters [{Os4(CO)8(RCCR)(η6-C6H6)}2(μ2-η2:η2-C6H8-1,3)] and [{Os4(CO)8(RCCR)(η6-C6H6)}2(μ2-η2:η2-C6H8-1,4)], respectively. The molecular structure of [{Os4(CO)8(MeCCMe)(η6-C6H6)}2(μ2-η2:η2-C6H8-1,3)] has been determined by single crystal X-ray diffraction, and represents the first example of two osmium cluster fragments linked by 1,3-cyclohexadiene through a μ2-η2:η2-bridge.

The reaction of the pendant hydroxyethyl group in the planar pentadentate macrocyclic ligand,1,11-bis(2’-hydroxyethyl)-4,8;12,16;17,21-trinitrilo-1,2,10,11-tetraazacyclohenicosa- 2,4,6,9,12,14,18,20-octaene (L 2 ), derived from the condensation of 2,6-pyridinedialdehyde with 6,6’-bis(2’ hydroxyethylhydrazino) -2,2’-bipyridine (L 1 ), has been investigated. Esterification reactions are facile, and the reaction of the hydroxyethyl-substituted macrocycle with thionyl chloride yields a chloroethyl derivative. Metal complexes of the new derivatized macrocyclic ligands L 3-6 having general formula ML 3-6 X 2 .nH 2 O (M = Mn, Fe, Co, Ni, Cu, Zn) are readily prepared.