Search

We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, idr6, and from the Gaia Early Data Release 3, edr3. We select a sample of main sequence, sub-giant, and giant stars in which Li abundance is measured by the Gaia-ESO survey, belonging to 57 open clusters with ages from 120~Myr to about 7 Gyr and to Milky Way fields, covering a range in [Fe/H] between -1.0 and +0.5dex. We study the behaviour of the Li abundances as a function of stellar parameters. We compare the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. The comparison with stellar evolution models confirms that classical models cannot reproduce the lithium abundances observed in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample, in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to ~2 dex), making lithium the best element to constrain stellar mixing processes in low-mass stars. For stars with well-determined masses, we find a better agreement between observed surface abundances and models with rotation-induced and thermohaline mixings, the former dominating during the main sequence and the first phases of the post-main sequence evolution and the latter after the bump in the luminosity function., Accepted for publication in A&A, 19 pages, 16 figures

Astrometry and photometry from Gaia and spectroscopic data from the Gaia-ESO Survey (GES) are used to identify the lithium depletion boundary (LDB) in the young cluster NGC 2232. A specialized spectral line analysis procedure was used to recover the signature of undepleted lithium in very low luminosity cluster members. An age of 38 ± 3 Myr is inferred by comparing the LDB location in absolute colour−magnitude diagrams (CMDs) with the predictions of standard models. This is more than twice the age derived from fitting isochrones to low-mass stars in the CMD with the same models. Much closer agreement between LDB and CMD ages is obtained from models that incorporate magnetically suppressed convection or flux-blocking by dark, magnetic starspots. The best agreement is found at ages of 45−50 Myr for models with high levels of magnetic activity and starspot coverage fractions >50 per cent, although a uniformly high spot coverage does not match the CMD well across the full luminosity range considered.

Context. NGC 2264 is a young cluster whose accretion properties can be investigated in detail by taking advantage of the FLAMES data in the context of the Gaia-ESO Survey. In fact, the analysis of the Hα emission line profile can provide us with information about the accretion and ejection activity of young stars. However, a strong nebular emission that contributes to the Hα emission can alter the profiles, with consequences for their physical interpretation. Aims. Our study is aimed at investigating the accretion and ejection properties of NGC 2264 by applying a proper treatment of the sky contribution to the Hα and forbidden emission lines (FELs; [SII] and [NII] doublets). Methods. We developed a tool, the OHαNA-method, to handle the strong nebular contribution and spectra with spurious profiles of the Hα and FELs, namely altered Hα profiles or absorption features artificially created where emission lines (FELs) are expected. We derived the quantitative measurements of relevant parameters to describe the accretion and ejection processes in young members of NGC 2264, focusing on reliable quantities derived from the width of the lines, which is relatively unaffected by the nebular emission, unlike the intensity peak, which can be altered significantly. Results. We derive the quantitative measurements related to the Hα emission line and discuss the comparison between the original and sky-subtracted spectra. We thus reveal possible profile alterations with consequences for their physical interpretation. Furthermore, we show the analysis of the variability for multi-epoch observations, also deriving the velocity of the infalling and outflowing plasma from the wings of the broad Hα emission line (in accreting stars). We also explore the mass accretion rate versus full width at zero intensity of the Hα line, namely Ṁ versus FWZI(Hα), a correlation based on the width of the emission line, which is expected to be more robust with respect to any measurement derived from the peak (e.g., Hα10%) and possibly altered by the nebular contribution. Conclusions. We are able to ascertain that more than 20% of the confirmed accretors, which have already been identified in NGC 2264, are affected by the alteration of their line profiles due to the contribution of the nebular emission. Therefore, this is an important issue to consider when investigating accretion and ejection processes in young stellar clusters. While a small fraction of spectra can be unequivocally classified as either unaffected by nebular emission or dominated by nebular emission, the majority (> 90%) represent intermediate cases whose spectral features have to be investigated in detail to derive reliable measurements of the relevant parameters and their physical implications.

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 ≲ 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 (τ < 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, Ti » I, Ti » II, Na » I, Mg » I, Al » I, Si » I, 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. © ESO 2020., This work is based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant "Premiale VLT 2012". The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. V.A. is supported by FCT -Fundacao para a Ciencia e a Tecnologia through national funds and by FEDER through COMPETE2020 -Programa Operacional Competitividade e Internacionalizacao by these grants: Investigador FCT contract nr. IF/00650/2015/CP1273/CT0001; UID/FIS/04434/2019; PTDC/FIS-AST/28953/2017 & POCI-01-0145-FEDER-028953 and PTDC/FIS-AST/32113/2017 & POCI-01-0145-FEDER-032113. F.J.E. acknowledges financial support from the Spanish MINECO/FEDER through grant AyA2017-84089. T.B. was supported by the project grant "The New Milky Way" from the Knut and Alice Wallenberg Foundation. U.H. acknowledges support from the Swedish National Space Agency (SNSA/Rymdstyrelsen). S.G.S acknowledges the support by Fundacao para a Ciencia e Tecnologia (FCT) through national funds and a research grant (project ref. UID/FIS/04434/2013, and PTDC/FIS-AST/7073/2014). S.G.S. also acknowledge the support from FCT through Investigador FCT contract of reference IF/00028/2014 and POPH/FSE (EC) by FEDER funding through the program -Programa Operacional de Factores de Competitividade -COMPETE.

In the era of large high-resolution spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, providing chemical abundances belonging to the different nucleosynthesis channels, and also providing constraints to stellar age. Some abundance ratios have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using, as calibrators, open star clusters observed by both the Gaia-ESO and APOGEE surveys. We use stellar parameters and abundances from the Gaia-ESO and APOGEE of the Galactic field and open cluster stars. Ages of star clusters are retrieved from the literature sources and validated using a common set of isochrones. We use the same isochrones to determine, for each age and metallicity, the surface gravity at which the first dredge-up and red giant branch bump occur. We study the effect of extra-mixing processes in our sample of giant stars, and we derive the mean [C/N] in evolved stars, including only stars without evidence of extra-mixing. Combining the Gaia-ESO and APOGEE samples of open clusters, we derive a linear relationship between [C/N] and logarithmic cluster ages. We apply our relationship to selected giant field stars in both Gaia-ESO and APOGEE. We find an age separation between thin and thick disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. With such empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. Isochrone fitting is less sensitive for giant than dwarf stars at the turn off. The present method can be thus considered as an additional tool to give an independent estimate of the age of giant stars, with uncertainties in their ages comparable to those obtained using isochrone fitting for dwarf stars., Comment: 28 pages, 24 figures. Accepted by A&A

The combination of precise radial velocities from multi-object spectroscopy and highly accurate proper motions from Gaia DR2 opens up the possibility for detailed 3D kinematic studies of young star-forming regions and clusters. Here, we perform such an analysis by combining Gaia-ESO Survey spectroscopy with Gaia astrometry for ∼900 members of the Lagoon Nebula cluster, NGC 6530. We measure the 3D velocity dispersion of the region to be 5.35+0.39 -0.34 km s, which is large enough to suggest the region is gravitationally unbound. The velocity ellipsoid is anisotropic, implying that the region is not sufficiently dynamically evolved to achieve isotropy, though the central part of NGC 6530 does exhibit velocity isotropy that suggests sufficient mixing has occurred in this denser part. We find strong evidence that the stellar population is expanding, though this is preferentially occurring in the declination direction and there is very little evidence for expansion in the right ascension direction. This argues against a simple radial expansion pattern, as predicted by models of residual gas expulsion. We discuss these findings in the context of cluster formation, evolution, and disruption theories.© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society., NJW acknowledges an STFC Ernest Rutherford Fellowship (grant number ST/M005569/1). RJP acknowledges support from the Royal Society in the form of a Dorothy Hodgkin Fellowship. AB acknowledges support from ICM (Iniciativa Cientifica Milenio) via the Nucleo Milenio de Formacion Planetaria. EJA acknowledges support from the Spanish Government Ministerio de Ciencia, Innovacion y Universidades though grant AYA2016-75 931-C2-1 and from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709).

Context. In very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. Determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the Hertzsprung-Russell diagram. Aims. In this context, we seek to derive accurate stellar ages for NGC 6530, the young cluster associated with the Lagoon Nebula to infer the star formation history of this region. Methods. We used the Gaia-ESO survey observations of the Lagoon Nebula, together with photometric literature data and Gaia DR2 kinematics, to derive cluster membership and fundamental stellar parameters. Using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members. Results. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. This classification is in agreement with the distances inferred from Gaia DR2 parallaxes for these objects. Finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. In addition, we find that the gravity-sensitive γ index distribution for the M-type stars is correlated with stellar age. Conclusions. For all members with Teff < 5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion or discs, i.e. classical T Tauri stars with excess (CTTSe), is similar to that of stars without accretion and without discs, i.e. weak T Tauri stars with photospheric emission (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by evidence of the decrease of the gravity-sensitive γ index as a function of stellar ages. The presence of a small age spread is also supported by the spatial distribution and kinematics of old and young members. In particular, members with accretion or discs, formed in the last 1 Myr, show evidence of subclustering around the cluster centre, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.© ESO 2019., The authors acknowledge support through the PRIN INAF 2014 funding scheme of the National Institute for Astrophysics (INAF) of the Italian Ministry of Education, University and Research (>The Gaia-ESO Survey>, P.I.: S. Randich). This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541.

(abridged) NGC6530 is a young cluster with a complex morphology and star-formation history. We present a statistical study of its global properties using a new large list of candidate members down to masses of 0.2-0.4 Msun and Gaia DR2 astrometry. We consider a wider sky region compared to previous studies, to investigate the whole cluster and its neighborhood. We study the distribution of extinction and age across the different regions, and obtain constraints on the star-formation history. Cluster membership is determined on the basis of X-ray data, H-alpha emission, near-IR and UV excesses from VPHAS+, UKIDSS and other surveys, and Gaia DR2 astrometry; we also use a novel method for photometric selection of M-type pre-main-sequence cluster members. The list of candidates includes nearly 3700 stars, of which we estimate ~2700 genuine NGC6530 members. Using Gaia parallaxes, the cluster distance is found to be 1325 pc, with errors of 0.5% (statistical) and 8.5% (systematic), in agreement with previous determinations. The cluster morphology and boundaries are established with great confidence, from members selected using different criteria. There is no diffuse population of members around the cluster, but there are minor member subgroups (associated with the stars 7 Sgr (F2II-III) and HD 164536 (O7.5V)) in addition to the two main groups in the cluster core and in the Hourglass nebula. We find a pattern of sequential star formation, between ages of, 21 pages, 22 figures, accepted for publication on Astronomy and Astrophysics

We aim to test a purely photometric approach to statistically identify a young clustered population embedded in a large population of field stars, with no prior knowledge on the nature of stars in the field. We conducted our blind test study on the NGC 2264 region, which hosts a well-known young cluster. We selected a large (4 sq. deg.) area around the NGC 2264 cluster, and assembled an extensive r,i,J catalog of the field from pre-existing large-scale surveys. We then mapped the stellar color locus on the (i-J, r-i) diagram to select M-type stars, which: i) comprise a significant fraction of the Galactic stellar population; ii) exhibit the strongest luminosity evolution from the PMS to the MS; iii) have r,i,J color properties that provide a direct and empirical estimate of A_V. A comparative analysis of the photometric and spatial properties of M-type stars as a function of A_V enabled us to probe the structure and stellar content of our field. We could identify two distinct populations: a diffuse field population and a clustered population. The presence of occulting material, spatially associated with the clustered population, allowed us to derive an estimate of its distance (800-900 pc) and age (~0.5-5 Myr), consistent with the literature parameters for the NGC 2264 star-forming region. The extracted clustered population exhibits a hierarchical structure, in excellent agreement with the NGC 2264 subregions reported in the literature. Our selection of clustered members is coherent with the literature census of the NGC 2264 cluster for about 95% of the objects in the inner regions of the field, where the contamination rate by field stars in our sample is only 2%. The method tested here can be readily applied to surveys like Pan-STARRS and the future LSST to undertake a first complete census of low-mass, young star populations down to distances of several kpc across the Galactic plane., 19 pages, 22 figures; accepted for publication in Astronomy & Astrophysics; abstract shortened for the ArXiv listing

Most stars born in clusters and recent results suggest that star formation (SF) preferentially occurs in subclusters. Studying the morphology and SF history of young clusters is crucial to understanding early SF. We identify the embedded clusters of young stellar objects (YSOs) down to M stars, in the HII regions RCW33, RCW32 and RCW27 of the Vela Molecular Ridge. Our aim is to characterise their properties, such as morphology and extent of the clusters in the three HII regions, derive stellar ages and the connection of the SF history with the environment. Through public photometric surveys such as Gaia, VPHAS, 2MASS and Spitzer/GLIMPSE, we identify YSOs with IR, Halpha and UV excesses, as signature of circumstellar disks and accretion. In addition, we implement a method to distinguish M dwarfs and giants, by comparing the reddening derived in several optical/IR color-color diagrams, assuming suitable theoretical models. Since this diagnostic is sensitive to stellar gravity, the procedure allows us to identify pre-main sequence stars. We find a large population of YSOs showing signatures of circumstellar disks with or without accretion. In addition, with the new technique of M-type star selection, we find a rich population of young M stars with a spatial distribution strongly correlated to the more massive population. We find evidence of three young clusters, with different morphology. In addition, we identify field stars falling in the same region, by securely classifying them as giants and foreground MS stars. We identify the embedded population of YSOs, down to about 0.1 Msun, associated with the HII regions RCW33, RCW32 and RCW27 and the clusters Vela T2, Cr197 and Vela T1, respectively, showing very different morphologies. Our results suggest a decreasing SF rate in Vela T2 and triggered SF in Cr197 and Vela T1., Comment: Accepted for publication in A&A; 20 pages, 22 figures, 6 tables

Context. The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been proposed to understand the formation of bound and unbound clusters and their evolution, and these can be tested by examining the kinematical and dynamical properties of clusters over a wide range of ages and masses. Aims. We use the Gaia-ESO Survey products to study four open clusters (IC 2602, IC 2391, IC 4665, and NGC 2547) that lie in the age range between 20 and 50 Myr. Methods. We employ the gravity index $\gamma$ and the equivalent width of the lithium line at 6708 $\AA$, together with effective temperature $\rm{T_{eff}}$, and the metallicity of the stars in order to discard observed contaminant stars. Then, we derive the cluster radial velocity dispersions $\sigma_c$, the total cluster mass $\rm{M}_{tot}$, and the half mass radius $r_{hm}$. Using the $Gaia$-DR1 TGAS catalogue, we independently derive the intrinsic velocity dispersion of the clusters from the astrometric parameters of cluster members. Results. The intrinsic radial velocity dispersions derived by the spectroscopic data are larger than those derived from the TGAS data, possibly due to the different masses of the considered stars. Using $\rm{M}_{tot}$ and $r_{hm}$ we derive the virial velocity dispersion $\sigma_{vir}$ and we find that three out of four clusters are supervirial. This result is in agreement with the hypothesis that these clusters are dispersing, as predicted by the "residual gas expulsion" scenario. However, recent simulations show that the virial ratio of young star clusters may be overestimated if it is determined using the global velocity dispersion, since the clusters are not fully relaxed., Comment: 14 pages, 6 figures

Aims. We present a spectroscopic study of the dynamics of the ionized and neutral gas throughout the Lagoon nebula (M 8), using VLT-FLAMES data from the Gaia-ESO Survey. The new data permit exploration of the physical connections between the nebular gas and the stellar population of the associated star cluster NGC 6530. Methods. We characterized through spectral fitting emission lines of Hα, [N II] and [S II] doublets, [O III], and absorption lines of sodium D doublet, using data from the FLAMES-Giraffe and UVES spectrographs, on more than 1000 sightlines toward the entire face of the Lagoon nebula. Gas temperatures are derived from line-width comparisons, densities from the [S II] doublet ratio, and ionization parameter from Hα/[N II] ratio. Although doubly-peaked emission profiles are rarely found, line asymmetries often imply multiple velocity components along the same line of sight. This is especially true for the sodium absorption, and for the [O III] lines. Results. Spatial maps for density and ionization are derived, and compared to other known properties of the nebula and of its massive stars 9 Sgr, Herschel 36 and HD 165052 which are confirmed to provide most of the ionizing flux. The detailed velocity fields across the nebula show several expanding shells, related to the cluster NGC 6530, the O stars 9 Sgr and Herschel 36, and the massive protostar M 8East-IR. The origins of kinematical expansion and ionization of the NGC 6530 shell appear to be different. We are able to put constrains on the line-of-sight (relative or absolute) distances between some of these objects and the molecular cloud. The data show that the large obscuring band running through the middle of the nebula is being compressed by both sides, which might explain its enhanced density. We also find an unexplained large-scale velocity gradient across the entire nebula. At larger distances, the transition from ionized to neutral gas is studied using the sodium lines.© 2017 ESO., This work was partly supported by the European Union FP7 program through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. T.Z. acknowledges support from the Slovenian Research Agency (research core funding No. P1-0188). F.J.-E. acknowledges financial support from the Spacetec-CM project (S2013/ICE-2822). M.T.C. acknowledges the financial support from the Spanish Ministerio de Economia y Competitividad, through grant AYA2016-75931-C2-1-P. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme.

We show that non-magnetic models for the evolution of pre-main-sequence (PMS) stars *cannot* simultaneously describe the colour-magnitude diagram (CMD) and the pattern of lithium depletion seen in the cluster of young, low-mass stars surrounding $\gamma^2$ Velorum. The age of 7.5+/-1 Myr inferred from the CMD is much younger than that implied by the strong Li depletion seen in the cluster M-dwarfs and the Li depletion occurs at much redder colours than predicted. The epoch at which a star of a given mass depletes its Li and the surface temperature of that star are both dependent on its radius. We demonstrate that if the low-mass stars have radii ~10 per cent larger at a given mass and age, then both the CMD and Li depletion pattern of the Gamma Vel cluster are explained at a common age of 18-21 Myr. This radius inflation could be produced by some combination of magnetic suppression of convection and extensive cool starspots. Models that incorporate radius inflation suggest that PMS stars similar to those in the Gamma Vel cluster, in the range 0.230 per cent) than inferred from conventional, non-magnetic models in the Hertzsprung-Russell diagram. Systematic changes of this size may be of great importance in understanding the evolution of young stars, disc lifetimes and the formation of planetary systems., Comment: 10 pages, accepted for publication in MNRAS

We present the first extensive X-ray study of the North-America and Pelican star-forming region (NGC7000/IC5070), with the aim of finding and characterizing its young stellar population. X-ray data from Chandra (four pointings) and XMM-Newton (seven pointings) were reduced and source detection was performed on each image. We complement the X-ray data with optical and near-IR data from the IPHAS, UKIDSS, and 2MASS catalogs, and with other published optical and Spitzer IR data. More than 700 X-ray sources are detected, the majority of which have an optical/NIR counterpart. This allows to identify young stars in different stages of formation. Less than 30% of X-ray sources are identified with a previously known young star. We argue that most X-ray sources with an optical/NIR counterpart, except perhaps for a few tens at near-zero reddening, are likely candidate members of the star-forming region, on the basis of both their optical/NIR magnitudes and colors, and of X-ray properties like spectrum hardness or flux variations. They are characterized by a wide range of extinction, and sometimes near-IR excesses, both of which prevent derivation of accurate stellar parameters. The optical color-magnitude diagram suggests ages between 1-10~Myrs. The X-ray members have a very complex spatial distribution with some degree of subclustering, qualitatively similar to that of previously known members. The distribution of X-ray sources relative to IR-excess objects found with Spitzer is sometimes suggestive of sequential star formation, especially near the Gulf of Mexico region, probably triggered by the O5 star illuminating the whole region. Around this latter star no enhancement in the young star density is found, in agreement with previous results. We also determine the local optical/IR reddening law, and compute an updated reddening map of the entire region., Comment: 24 pages, 38 figures, 5 tables; accepted by A&A

Sco OB2 is the nearest OB association, extending over approximately 2000 sq.deg. on the sky. Only its brightest members are already known (from Hipparcos) across its entire size, while studies of its lower-mass population refer only to small portions of its extent. In this work we exploit the capabilities of Gaia DR2 measurements to search for Sco OB2 members across its entire size and down to the lowest stellar masses. We use both Gaia astrometric and photometric data to select association members, using minimal assumptions derived mostly from the Hipparcos studies. Gaia resolves small details in both the kinematics of individual Sco OB2 subgroups and their distances from the Sun. We develop methods to explore the 3D kinematics of stellar populations covering large sky areas. We find ~11000 pre-main sequence (PMS) Sco OB2 members (with, 27 pages, 37 figures. Accepted for publication in Astronomy and Astrophysics

The discovery of lithium-rich giants contradicts expectations from canonical stellar evolution. Here we report on the serendipitous discovery of 20 Li-rich giants observed during the Gaia-ESO Survey, which includes the first nine Li-rich giant stars known towards the CoRoT fields. Most of our Li-rich giants have near-solar metallicities, and stellar parameters consistent with being before the luminosity bump. This is difficult to reconcile with deep mixing models proposed to explain lithium enrichment, because these models can only operate at later evolutionary stages: at or past the luminosity bump. In an effort to shed light on the Li-rich phenomenon, we highlight recent evidence of the tidal destruction of close-in hot Jupiters at the sub-giant phase. We note that when coupled with models of planet accretion, the observed destruction of hot Jupiters actually predicts the existence of Li-rich giant stars, and suggests Li-rich stars should be found early on the giant branch and occur more frequently with increasing metallicity. A comprehensive review of all known Li-rich giant stars reveals that this scenario is consistent with the data. However more evolved or metal-poor stars are less likely to host close-in giant planets, implying that their Li-rich origin requires an alternative explanation, likely related to mixing scenarios rather than external phenomena., This work is based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the $\textit{Gaia}$-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and the Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR) in the form of the grant Premiale VLT 2012 and the Chemical and Dynamical Evolution of the Milky Way and Local Group Galaxies (prot. 2010LY5N2T). The results presented here benefit from discussions held during the $\textit{Gaia}$-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. GR acknowledges support from the project grant ‘The New Milky Way’ from the Knut and Alice Wallenberg Foundation. GMK is supported by the Royal Society as a Royal Society University Research Fellow. LS acknowledges support provided by the Chilean Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics, MAS. Funding for the Stellar Astrophysics Centre is provided by the Danish National Research Foundation. The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (Grant agreement no. 267864). VSA acknowledges support from VILLUM FONDEN (research grant 10118). SLM acknowledges support from the Australian Research Council through DECRA fellowship DE140100598. TM acknowledges financial support from Belspo for contract PRODEX Gaia-DPAC. JM acknowledges the support from the European Research Council Consolidator Grant funding scheme (project STARKEY, G.A. no. 615604). This research has made use of the ExoDat Database, operated at LAM-OAMP, Marseille, France, on behalf of the CoRoT/Exoplanet programme. This research made use of astropy, a community-developed core python package for Astronomy (Astropy Collaboration et al. 2013). This research has made use of NASA's Astrophysics Data System Bibliographic Services., This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw1512

Old open clusters are very useful targets to investigate mechanisms responsible for lithium (Li) depletion during the main sequence. Comparison of the Li abundances in clusters of different age allows us to understand the efficiency of the Li destruction process. Our goal is the determination of membership and Li abundance in a sample of candidate members of the open cluster NGC 3960 (age ~1 Gyr), with the aim to fill the gap between 0.6 and 2 Gyr in the empirical description of the behavior of the average Li abundance as a function of the stellar age. We use VLT/FLAMES Giraffe spectra to determine the radial velocities and thus the membership of a sample of 113 photometrically selected candidate cluster members. From the analysis of the Li line we derive Li abundances for both cluster members and non-members. 39 stars have radial velocity consistent with membership, with an expected fraction of contaminating field stars of about 20%. Li is detected in 29 of the RV members; we consider these stars as cluster members, while we make the reasonable assumption that the remaining 10 RV members without Li, are among the contaminating stars. Li abundances of the stars hotter than about 6000 K are similar to those of stars in the Hyades, while they are slightly smaller for cooler stars. This confirms that NGC 3960 is older than the Hyades. The average Li abundance of stars cooler than about 6000 K indicates that the Li Pop. I plateau might start already at ~1 Gyr rather than 2 Gyr that is the upper limit previously derived in the literature. We also find that the fraction of field stars with high Li abundance (>1.5) is about one third of the whole sample, which is in agreement with previous estimates. The fraction of contaminating field stars is consistent with that previously derived by us from photometry., 12 pages,10 figures, in press in Astronomy and Astrophysics

This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategies are implemented to deal with fast rotation, accretion signatures, chromospheric activity, and veiling. The analysis carried out on spectra acquired in young clusters' fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide with confidence stellar parameters for the much larger GIRAFFE sample. Precisions are estimated to be $\approx$ 120 K r.m.s. in Teff, $\approx$0.3 dex r.m.s. in logg, and $\approx$0.15 dex r.m.s. in [Fe/H], for both the UVES and GIRAFFE setups., 22 pages, 18 figures, accepted for publication on A&A

Aims: One of the goals of the Gaia-ESO Survey (GES), which is conducted with FLAMES at the VLT, is the census and the characterization of the low-mass members of very young clusters and associations. We conduct a comparative study of the main properties of the sources belonging to γ Velorum (γ Vel) and Chamaeleon I (Cha I) young associations, focusing on their rotation, chromospheric radiative losses, and accretion. Methods: We used the fundamental parameters (effective temperature, surface gravity, lithium abundance, and radial velocity) delivered by the GES consortium in the first internal data release to select the members of γ Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 γ Vel members and 74 Cha I members were studied. The procedure adopted by the GES to derive stellar fundamental parameters also provided measures of the projected rotational velocity (vsini). We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the vsini of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the Hα and Hβ lines. The Hα line was also used for identifying accreting objects, on the basis of its EW and the width at the 10% of the line peak (10%W), and for evaluating the mass accretion rate (Ṁacc). Results: The distribution of vsini for the members of γ Vel displays a peak at about 10 km s-1 with a tail toward faster rotators. There is also some indication of a different vsini distribution for the members of its two kinematical populations. Most of these stars have Hα fluxes corresponding to a saturated activity regime. We find a similar distribution, but with a narrower peak, for Cha I. Only a handful of stars in γ Vel display signatures of accretion, while many more accretors were detected in the younger Cha I, where the highest Hα fluxes are mostly due to accretion, rather than to chromospheric activity. Accreting and active stars occupy two different regions in a Teff-flux diagram and we propose a criterion for distinguishing them. We derive Ṁacc in the ranges 10-11-10-9 M☉ yr-1 and 10-10-10-7 M☉ yr-1 for γ Vel and Cha I accretors, respectively. We find less scatter in the Ṁacc - M⋆ relation derived through the Hα EWs, when compared to the Hα10%W diagnostics, in agreement with other authors. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002.Tables 5, 6, and Appendix A are available in electronic form at http://www.aanda.orgTables 2-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A4

We discuss the properties of Hα emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of Hα line profiles with the introduction of a simplified classification scheme. All in all, we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: single-component emission, emission blend, sharp emission peaks, double emission, P-Cygni, inverted P-Cygni, self-absorption, and emission in absorption. We have more than one observation for 1430 stars in our sample, thus allowing a quantitative discussion of the degree of variability of Hα emission profiles, which is expected for young, active objects. We present a catalogue of stars with properties of their Hα emission line profiles, morphological classification, analysis of variability with time and the supplementary information from the SIMBAD, VizieR, and ADS databases. The records in SIMBAD indicate the presence of Hα emission for roughly 25% of all stars in our catalogue, while at least 305 of them have already been more thoroughly investigated according to the references in ADS. The most frequently identified morphological categories in our sample of spectra are emission blend (23%), emission in absorption (22%), and self-absorption (16%). Objects with repeated observations demonstrate that our classification into discrete categories is generally stable through time, but categories P-Cygni and self-absorption seem less stable, which is the consequence of discrete classification rules, as well as of the fundamental change in profile shape. Such records of emission stars can be valuable for automatic pipelines in large surveys, where it may prove very useful for pinpointing outliers when calculating general stellar properties and elemental abundances. They can be used in studies of star formation processes, interacting binaries, and other fields of stellar physics. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002.Full Tables D.1-D.3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A52

Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria,to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the Li I 6707.8 Angstroms line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray data to study the cluster membership. Optical-IR data and Halpha spectra, these latter available for a subsample of our targets, are used to classify CTTS and WTTS and to compare the properties of stars with and without disks. We find a total of 237 certain members including 53 binaries. The rotational velocity distributions of stars with IR excesses are statistically different from that of stars without IR excesses, while the fraction of binaries with disks is significantly smaller than that of single stars. Stars with evidence for accretion show circumstellar disks; youth of cluster members is confirmed by the lithium abundance consistent with the initial content. As indicated by the disk-locking picture, stars with disks have in general rotational velocities lower than stars without disks. Binaries in NGC 6530 seem have undergone a significant disk evolution., Comment: 18 pages, 17 figures, in press in Astronomy and Astrophysics

Full list of authors: Tang, B.; Geisler, D.; Friel, E.; Villanova, S.; Smiljanic, R.; Casey, A. R.; Randich, S.; Magrini, L.; San Roman, I.; Muñoz, C.; Cohen, R. E.; Mauro, F.; Bragaglia, A.; Donati, P.; Tautvaišien*error*ė, G.; Drazdauskas, A.; Ženovienė, R.; Snaith, O.; Sousa, S.; Adibekyan, V. Costado, M. T.; Blanco-Cuaresma, S.; Jiménez-Esteban, F.; Carraro, G.; Zwitter, T.; François, P.; Jofrè, P.; Sordo, R.; Gilmore, G.; Flaccomio, E.; Koposov, S.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Bayo, A.; Damiani, F.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Worley, C. C.; Zaggia, S., Milky Way open clusters are very diverse in terms of age, chemical composition, and kinematic properties. Intermediate-age and old open clusters are less common, and it is even harder to find them inside the solar Galactocentric radius, due to the high mortality rate and strong extinction inside this region. NGC 6802 is one of the inner disk open clusters (IOCs) observed by the Gaia-ESO survey (GES). This cluster is an important target for calibrating the abundances derived in the survey due to the kinematic and chemical homogeneity of the members in open clusters. Using the measurements from Gaia-ESO internal data release 4 (iDR4), we identify 95 main-sequence dwarfs as cluster members from the GIRAFFE target list, and eight giants as cluster members from the UVES target list. The dwarf cluster members have a median radial velocity of 13.6 ± 1.9 km s, while the giant cluster members have a median radial velocity of 12.0 ± 0.9 km s and a median [Fe/H] of 0.10 ± 0.02 dex. The color-magnitude diagram of these cluster members suggests an age of 0.9 ± 0.1 Gyr, with (m-M) = 11.4 and E(B-V) = 0.86. We perform the first detailed chemical abundance analysis of NGC 6802, including 27 elemental species. To gain a more general picture about IOCs, the measurements of NGC 6802 are compared with those of other IOCs previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs. These elements are compared with nucleosynthetic models as a function of cluster turn-off mass. The α, iron-peak, and neutron-capture elements are also explored in a self-consistent way. © ESO, 2017., Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita e della Ricerca (MIUR) in the form of the grant "Premiale VLT 2012". The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. We thank the anonymous referee for insightful comments. D.G., S.V., and B.T. gratefully acknowledges support from the Chilean BASAL Centro de Excelencia en Astrofisica y Tecnologias Afines (CATA) grant PFB-06/2007. C.M. acknowledges support from CONICYT-PCHA/Doctorado Nacional/2014-21141057. R.E.C. acknowledges funding from Gemini-CONICYT for Project 32140007. F.M. gratefully acknowledges the support provided by Fondecyt for project 314017. This work was partly supported (A.R.C.) by the European Union FP7 programme through grant number 320360. This work was partly supported (A.D., G.T., R.Z.) by the grant from the Research Council of Lithuania (MIP082/2015). S.G.S. acknowledges the support from FCT through Investigador FCT contract of reference IF/00028/2014 and the support from FCT through the project PTDC/FIS-AST/7073/2014. C.L. gratefully acknowledges financial support from the European Research Council (ERC-CoG-646928, Multi-Pop, PI: N. Bastian). V.A. acknowledges the support from the FCT (Portugal) in the form of the grant SFRH/BPD/70574/2010, the support by FCT through national funds (Refs. PTDC/FIS-AST/7073/2014 and PTDC/FIS-AST/1526/2014) and by FEDER through COMPETE2020 (Refs. POCI-01-0145-FEDER-016880 and POCI-01-0145-FEDER-016886).

NGC 4815 is a populous ~500 Myr open cluster at a Galactocentric radius of 7 kpc observed in the first six months of the Gaia-ESO Survey. Located in the inner Galactic disk, NGC 4815 is an important tracer of the abundance gradient, where few intermediate age open clusters are found. We use the survey derived radial velocities, stellar atmospheric parameters, metallicity, and elemental abundances for stars targeted as potential members of this cluster to carry out an analysis of cluster properties. The radial velocity distribution of stars in the cluster field is used to define the cluster systemic velocity and derive likely cluster membership for stars observed by the Gaia-ESO Survey. We investigate the distributions of Fe and Fe-peak elements, alpha-elements, and the light elements Na and Al and characterize the cluster's internal chemical homogeneity comparing it to the properties of radial velocity non-member stars. Utilizing these cluster properties, the cluster color-magnitude diagram is analyzed and theoretical isochrones are fit to derive cluster reddening, distance, and age. NGC 4815 is found to have a mean [Fe/H]=+0.03. Elemental abundances of cluster members show typically small internal variation, with internal dispersions of ~0.05 dex. [Ca/Fe] and [Si/Fe] show solar ratios, but [Mg/Fe] is moderately enhanced, while [Ti/Fe] appears slightly deficient. As with many open clusters, [Na/Fe] and [Al/Fe] are enhanced, [Na/Fe] significantly so, although the role of internal mixing and the assumption of LTE in the analysis remain to be investigated. From isochrone fits to color-magnitude diagrams, we find a cluster age of 0.5 to 0.63 Gyr, a reddening of E(B-V) = 0.59 to 0.65, and a true distance modulus (m-M) = 11.95 to 12.20, depending on the choice of theoretical models, leading to a Galactocentric distance of 6.9 kpc., 10 pages, 8 figures, published in Astronomy & Astrophysics

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., Comment: 17 pages, 11 figures, A&A accepted

We study spectral diagnostics available from optical spectra with R=17000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the gamma Vel young cluster, in order to determine the fundamental parameters of these stars. We define a set of spectroscopic indices, sampling TiO bands, H-alpha core and wings, and many temperature- and gravity-sensitive lines. Combined indices tau (gamma) are also defined as Teff (log g) indicators over a wide spectral-type range. H-alpha emission-line indices are also chromospheric activity or accretion indicators. A metallicity-sensitive index is also defined. These indices enable us to find a clear difference between gravities of main-sequence and pre-main-sequence stars (as well as giant stars): the (gamma,tau) diagram is thus argued to be a promising distance-independent age measurement tool for young clusters. Our indices were quantitatively calibrated by means of photometry and literature reference spectra (from UVES-POP and ELODIE 3.1 Libraries, and other datasets), over a wide range of stellar parameters. The ability of our indices to select peculiar, or other rare classes of stars is also established. Finally, our gravity determinations support the existence of an older pre-main-sequence population in the gamma Vel sky region, in agreement with the lithium depletion pattern of those stars (abridged).

Context. Recent metallicity determinations in young open clusters and star-forming regions suggest that the latter may be characterized by a slightly lower metallicity than the Sun and older clusters in the solar vicinity. However, these results are based on small statistics and inhomogeneous analyses. The Gaia-ESO Survey is observing and homogeneously analyzing large samples of stars in several young clusters and star-forming regions, hence allowing us to further investigate this issue. Aims. We present a new metallicity determination of the Chamaeleon I star-forming region, based on the products distributed in the first internal release of the Gaia-ESO Survey. Methods. 48 candidate members of Chamaeleon I have been observed with the high-resolution spectrograph UVES. We use the surface gravity, lithium line equivalent width and position in the Hertzsprung-Russell diagram to confirm the cluster members and we use the iron abundance to derive the mean metallicity of the region. Results. Out of the 48 targets, we confirm 15 high probability members. Considering the metallicity measurements for 9 of them, we find that the iron abundance of Chamaeleon I is slightly subsolar with a mean value [Fe/H]=-0.08+/-0.04 dex. This result is in agreement with the metallicity determination of other nearby star-forming regions and suggests that the chemical pattern of the youngest stars in the solar neighborhood is indeed more metal-poor than the Sun. We argue that this evidence may be related to the chemical distribution of the Gould Belt that contains most of the nearby star-forming regions and young clusters., Comment: 13 pages, 11 figures, 3 tables, Accepted for publication in Astronomy & Astrophysics

Mechanisms regulating the origin of X-rays in YSOs and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC6611. At 1750 pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age, Accepted in ApJ

The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.

We studied three Galactic open clusters (OC) spanning a range of age of 1 Gyr in order to compare their Mass Function (MF). In all cases, we analyzed optical multi-band images to obtain the color-magnitude diagrams (CMD). Several theoretical stellar evolution models were considered to determine distance and age of the OCs and to convert the Luminosity Function (LF) into MF. Different membership criteria were used for each OC based on cluster properties and Xray data and/or photometric IR data available in literature. The adopted methods and the comparison of the Initial Mass Functions (IMF) derived for the three OCs are presented.

Context: the observation of young stars with circumstellar disks suggests that the disks are dissipated, starting from the inner region, by the radiation of the central star and eventually by the formation of rocky planetesimals, over a time scale of several million years. It was also shown that strong UV radiation emitted by nearby massive stars can heat a circumstellar disk up to some thousand degrees, inducing the photoevaporation of the gas. This process strongly reduces the dissipation time scale. Aims: we study whether there exists a correlation between the spatial distribution of stars with circumstellar disks and the position of massive stars with spectral class earlier than B5, in the open cluster NGC 6611. Methods: we created a multiband catalog of the cluster, down to V~23, using optical data from a WFI observation at 2.2m of ESO in the BVI bands, the 2MASS public point source catalog and an archival X-ray observation made with CHANDRA/ACIS. We selected the stars with infrared excess (due to the emission of a circumstellar disk) using suitable color indices independent of extinction, and studied their spatial distribution. Results: the spatial distribution of the stars with K band excess (due to the presence of a circumstellar disk) is anti correlated with that of the massive stars: the disks are more frequent at large distances from these stars. We argue that this is in agreement with the hypothesis that the circumstellar disks are heated by the UV radiation from the massive stars and photoevaporated., 16 pages, 14 figures (high quality figures available at: "http://www.astropa.unipa.it/Library/preprint.html". Accepted for publication in A&A

Context. Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. Aims. We select cluster members using different membership criteria, to study the properties of pre-main sequence stars with or without circumstellar disks. Methods. We use intermediate resolution spectra including the Li I 6707.8 $\AA$ line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray data to study the cluster membership. Optical-IR data and H α spectra, these latter available for a subsample of our targets, are used to classify CTTS and WTTS and to compare the properties of stars with and without disks. Results. We find a total of 237 certain members including 53 binaries. The rotational velocity distributions of stars with IR excesses are statistically different from that of stars without IR excesses, while the fraction of binaries with disks is significantly smaller than that of single stars. Stars with evidence of accretion show circumstellar disks; youth of cluster members is confirmed by the lithium abundance consistent with the initial content. Conclusions. As indicated by the disk-locking picture, stars with disks in general have rotational velocities lower than stars without disks. Binaries in NGC 6530 seem have undergone significant disk evolution.

We report on preliminary results of VLT/FLAMES observations of the old open clusters NGC 2506, Mel 66 and Cr 261, obtained as part of our Guaranteed Time on this instrument. We focus in particular on the very old cluster Cr 261, one of the oldest open clusters in the Galaxy. We compare the derived Li abundances with those of other old clusters, and we discuss briefly Li depletion on the main-sequence from the age of the Hyades to ∼8 Gyr. 1 The GTO Program on Open Clusters With the advent of the multi-object spectrograph FLAMES at the VLT [13], the study of open clusters has received a great boost due both to the larger telescope area and to the multiplexing capability offered by the new instrument. Not only it is now possible to reach at intermediate resolution (R∼20,000) fainter objects and more distant clusters, but it is also possible to obtain in one shot spectra of ∼130 objects, with an increase in observational efficiency of several hundreds with respect to single-object spectrographs on 4m-class telescopes. Open clusters are among the most suitable targets for observations with FLAMES since they provide homogeneous samples of stars of the same age and chemical composition over projected areas in the sky typically smaller, except for the closest clusters, than the FLAMES field-of-view (25 arcmin diameter). In return to the Italian participation in the development of FLAMES, the Ital-FLAMES Consortium obtained 11 guaranteed nights that were devoted to various science programs. 3 of these nights were used for observations of open clusters of different ages and metallicities (P.I. R. Pallavicini) with the purpose of investigating Li abundances, metallicities and membership with GIRAFFE, and Fe and α-element abundances with the fiber link to UVES. Our sample includes young clusters such as the Orion Nebula Cluster, NGC 6530 (a few Myr in age) and Blanco 1 (∼100 Myr), all observed also in X-rays with Chandra and/or XMM-Newton, as well as the old clusters NGC 2506, Mel 66 and Cr 261 (all older than the Hyades). Here we focus on the old clusters which offer a unique opportunity for investigating Li depletion and non-standard mixing mechanisms in dwarf stars during their main-sequence (MS) evolution. 182 R. Pallavicini et al. 2 Li in Old Clusters The scientific motivations of our study were reviewed recently by several authors (e.g. [1]; [6]; [20]; [12]). In brief, observations of clusters of different ages and metallicities, carried out mostly with 4m-class telescopes and, to a much less extent so far, with HIRES at Keck and UVES at the VLT, have shown that solar-type stars suffer Li depletion on the MS, contrary to expectations of standard models, i.e. models that assume convection as the only mixing mechanism on the MS. Moreover, while the Hyades (age ∼600 Myr) and most clusters older than the Hyades observed so far (e.g. [22]; [18]; [19]; [21]) show a tight Li vs. Teff relationship, with little or no scatter, a large Li spread is observed in the solar-age cluster M 67 ([15]; [7]) as well as in field stars [14]. In particular, the low Li abundance of the present Sun, which is two orders of magnitude lower than the Li abundance of T-Tauri stars and of the meteorites, remains totally unexplained. This feature, together with the presence of a Li spread in M 67 and of Li depletion on the MS, with little or no observed dependence on metallicity ([6]; [21]), indicates the occurrence of non-standard mixing mechanisms (e.g. rotational mixing, diffusion, mass loss, gravitational waves) in addition to convection (e.g. [17]; [1]; and references therein). As part of our GTO program on FLAMES, we have observed the open clusters NGC 2506 (age ∼2 Gyr, [9]), Mel 66 (∼4 Gyr, [8]) and Cr 261 (∼8 Gyr, [4]; [2]). The observations were carried out in May and Dec 2003 (for Cr 261 and Mel 66, respectively) and Feb 2004 (for NGC 2506). Astrometry and photometry were taken from EIS imaging observations [11] for NGC 2506 and Mel 66 and from dedicated WFI observations at the ESO/MPA 2.2m telescope for Cr 261. The data, which comprise more than 100 objects for each cluster, were obtained with the GIRAFFE spectrograph in the MEDUSA mode (R∼20,000) using the grating setting HR15 centered at 679.7 nm (i.e. in the Li region). 7 bright members of each cluster were observed at a higher resolution (R∼50,000) with the fiber-link to UVES. The GIRAFFE spectra were reduced with the standard pipeline and are now being analysed to derive radial velocities, Li abundances, and metallicities for turn-off (TO) and lower MS stars. Preliminary results on Li abundances in Cr 261 are presented here. Results for the other clusters will be reported elsewhere (Spano et al., in preparation). 3 The Old Open Cluster Cr 261 Cr 261 is one of the oldest open clusters in the Galaxy, with an estimated age ranging from ∼7 to ∼11 Gyr ([5]; [16]; [4]). The metallicity, derived from both low-resolution and high-resolution spectra, is slightly subsolar ([Fe/H]=−0.2; [3]; [2]) and the reddening is highly uncertain, with quoted E(B − V ) values ranging from 0.22 to 0.34 ([5]; [10]; [4]). Proper motion and/or radial velocity memberships are not known, and the contamination by field stars is high. However, the TO and MS are clearly visible in the color-magnitude diagrams with the TO at V 16.7, (B−V ) 0.85, (V −I) 0.95 (cf. [4]). We have observed with Multi-Object Spectroscopy of Open Clusters with FLAMES 183 0.50 0.55 0.60 0.65 0.70 0.75 0 50 10 0 15 0 (B − V)o (reddening=0.34) E .W . L iI+ F eI ( m A ) Fig. 1. Li equivalent widths vs. dereddened (B − V )o color for MS stars of Cr 261. Teff (K) lo g A (L i) + 12 6400 6200 6000 5800 5600 5400 5200 5000 0. 0 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 Collinder 261 (7−11 Gyr), this study E(B−V)=0.34 Hyades (600 Myr), Thorburn et al. 1993 M 67 (5 Gyr), Jones et al. 1999 Fig. 2. Li abundances vs. Teff for MS stars in Cr 261 (filled circles), compared to the Hyades (asterisks, [22]) and M 67 (squares, [7]). A reddening E(B−V )=0.34 has been

In the context of a large observational project on old open clusters, we employed FLAMES + UVES on VLT UT2 to collect new high resolution spectra for giant stars in 7 clusters with the aim of investigating the radial abundance distributions in the Galactic disk. The gradients of Fe, α and Fe-peak elements and their evolution with Galactic age are indeed one of the most critical constraints to the star formation history in the Galactic disk and to Galactic chemical evolution models. We present here our preliminary results on the metallicity and abundance ratios for red clump stars in the ∼1 Gyr old cluster NGC 3960, located at a Galactocentric distance $R_{gc}\sim8$ kpc.

Mechanisms involved in the star formation process and in particular the duration of the different phases of the cloud contraction are not yet fully understood. Photometric data alone suggest that objects coexist in the young cluster NGC6530 with ages from ~1 Myr up to 10 Myrs. We want to derive accurate stellar parameters and, in particular, stellar ages to be able to constrain a possible age spread in the star-forming region NGC6530. We used low-resolution spectra taken with VIMOS@VLT and literature spectra of standard stars to derive spectral types of a subsample of 94 candidate members of this cluster. We assign spectral types to 86 of the 88 confirmed cluster members and derive individual reddenings. Our data are better fitted by the anomalous reddening law with R$_{\rm V}$=5. We confirm the presence of strong differential reddening in this region. We derive fundamental stellar parameters, such as effective temperatures, photospheric colors, luminosities, masses, and ages for 78 members, while for the remaining 8 YSOs we cannot determine the interstellar absorption, since they are likely accretors, and their V-I colors are bluer than their intrinsic colors. The cluster members studied in this work have masses between 0.4 and 4 M$_\odot$ and ages between 1-2 Myrs and 6-7 Myrs. We find that the SE region is the most recent site of star formation, while the older YSOs are loosely clustered in the N and W regions. The presence of two distint generations of YSOs with different spatial distribution allows us to conclude that in this region there is an age spread of ~6-7 Myrs. This is consistent with the scenario of sequential star formation suggested in literature., 23 pages, 16 Postscript figures, 5 tables. Accepted for publication in Astronomy and Astrophysics