- ID:
- ivo://CDS.VizieR/J/A+A/601/A97
- Title:
- Gaia-ESO Survey: Cha I members
- Short Name:
- J/A+A/601/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Investigating the physical mechanisms driving the dynamical evolution of young star clusters is fundamental to our understanding of the star formation process and the properties of the Galactic field stars. The young (~2Myr) and partially embedded cluster Chamaeleon I is one of the closest laboratories to study the early stages of star cluster dynamics in a low-density environment. The aim of this work is to study the structural and kinematical properties of this cluster combining parameters from the high-resolution spectroscopic observations of the Gaia-ESO Survey with data from the literature. Our main result is the evidence of a large discrepancy between the velocity dispersion ({sigma}_stars_=1.14+/-0.35km/s) of the stellar population and the dispersion of the pre-stellar cores (~0.3km/s) derived from submillimeter observations. The origin of this discrepancy, which has been observed in other young star clusters is not clear. It has been suggested that it may be due to either the effect of the magnetic field on the protostars and the filaments, or to the dynamical evolution of stars driven by two-body interactions. Furthermore, the analysis of the kinematic properties of the stellar population put in evidence a significant velocity shift (~1~km/s) between the two sub-clusters located around the North and South main clouds of the cluster. This result further supports a scenario, where clusters form from the evolution of multiple substructures rather than from a monolithic collapse.Using three independent spectroscopic indicators (the gravity indicator {gamma}, the equivalent width of the Li line at 6708{AA}, and the H{alpha} 10% width), we performed a new membership selection. We found six new cluster members all located in the outer region of the cluster, proving that Chamaeleon I is probably more extended than previously thought. Starting from the positions and masses of the cluster members, we derived the level of substructure Q, the surface density {Sigma} and the level of mass segregation {Lambda}_MSR_ of the cluster. The comparison between these structural properties and the results of N-body simulations suggests that the cluster formed in a low density environment, in virial equilibrium or supervirial, and highly substructured.
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- ID:
- ivo://CDS.VizieR/J/A+A/612/A99
- Title:
- Gaia-ESO Survey in 7 open star cluster fields
- Short Name:
- J/A+A/612/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017A&A...601A..19G, Cat. J/A+A/601/A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.
- ID:
- ivo://CDS.VizieR/J/A+A/574/L7
- Title:
- Gaia-ESO Survey: Li-rich stars in NGC2547
- Short Name:
- J/A+A/574/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby (distance ~350-400pc), rich Vela OB2 association, includes gamma^2^ Velorum, one of the most massive binaries in the solar neighborhood, and is an excellent laboratory for investigating the formation and early evolution of young clusters. Recent Gaia-ESO survey observations led to the discovery of two kinematically distinct populations in the young (10-15Myr) cluster immediately surrounding gamma^2^ Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35Myr cluster located two degrees south of gamma^2^ Velorum. The radial velocity distribution of lithium-rich pre-main sequence stars shows a secondary population, kinematically distinct and younger than NGC 2547. The radial velocities, lithium absorption lines, and the positions in a color-magnitude diagram of this secondary population are consistent with those of one of the components discovered around gamma^2^ Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degrees in the Vela OB2 association. This population could have originally been part of a cluster around gamma^2^ Velorum that expanded after gas expulsion, or formed in a less dense environment spread over the whole Vela OB2 region.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A17
- Title:
- Gaia-ESO Survey: NGC6705
- Short Name:
- J/A+A/569/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations. Studying the chemical homogeneity of the most massive open clusters is needed to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGC 6705, which is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGC 6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A37
- Title:
- Gaia-ESO Survey. Parameters for cluster members
- Short Name:
- J/A+A/591/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the metallicity gradient inside the solar circle (R_GC_<8kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. The GES open clusters exhibit a radial metallicity gradient of -0.10+/-0.02dex/kpc, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range R_GC_~6-12kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. We find no evidence for a steepening of the inner disk metallicity gradient inside the solar circle as earlier studies indicated. The age-metallicity relation shown by the clusters is consistent with that predicted by chemical evolution models that include the effects of radial migration, but a more detailed comparison between cluster observations and models would be premature.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A55
- Title:
- Gaia-ESO Survey: Tr 20, NGC4815, NGC6705
- Short Name:
- J/A+A/573/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia-ESO Public Spectroscopic Survey will observe a large sample of clusters and cluster stars, covering a wide age-distance-metallicity-position-density parameter space. We aim to determine C, N, and O abundances in stars of Galactic open clusters of the Gaia-ESO survey and to compare the observed abundances with those predicted by current stellar and Galactic evolution models. In this pilot paper, we investigate the first three intermediate-age open clusters. High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO VLT, were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C_2_ band heads at 5135 and 5635.5{AA}. The wavelength interval 6470-6490{AA}, with CN features, was analysed to determine nitrogen abundances. Oxygen abundances were determined from the [OI] line at 6300{AA}. The mean values of the elemental abundances in Trumpler 20 as determined from 42 stars are: [Fe/H]=0.10+/-0.08 (s.d.), [C/H]=-0.10+/-0.07, [N/H]=0.50+/-0.07, and consequently C/N=0.98+/-0.12. We measure from five giants in NGC 4815: [Fe/H]=-0.01+/-0.04, [C/H]=-0.17+/-0.08, [N/H]=0.53+/-0.07, [O/H]=0.12+/-0.09, and C/N=0.79+/-0.08. We obtain from 27 giants in NGC 6705: [Fe/H]=0.0+/-0.05, [C/H]=-0.08+/-0.06, [N/H]=0.61+/-0.07, [O/H]=0.13+/-0.05, and C/N=0.83+/-0.19. The C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolutionary models. For the corresponding stellar turn-off masses from 1.9 to 3.3M_{sun}_, the observed C/N ratio values are very close to the predictions of standard first dredge-up models as well as to models of thermohaline extra-mixing. They are not decreased as much as predicted by the recent model in which the thermohaline- and rotation-induced extra-mixing act together. The average [O/H] abundance ratios of NGC 4815 and NGC 6705 are compared with the predictions of two Galactic chemical evolution models. The data are consistent with the evolution at the solar radius within the errors. The first results of CNO determinations in open clusters show the potential of the Gaia-ESO Survey to judge stellar and Galactic chemical evolution models and the validity of their physical assumptions through a homogeneous and detailed spectral analysis.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A68
- Title:
- Gaia-ESO Survey. Trumpler 23
- Short Name:
- J/A+A/598/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Trumpler 23 is a moderately populated, intermediate-age open cluster within the solar circle at a R_GC_~6kpc. It is in a crowded field very close to the Galactic plane and the color-magnitude diagram shows significant field contamination and possible differential reddening; it is a relatively understudied cluster for these reasons, but its location makes it a key object for determining Galactic abundance distributions. New data from the Gaia-ESO Survey enable the first ever radial velocity and spectroscopic metallicity measurements for this cluster. We aim to use velocities to isolate cluster members, providing more leverage for determining cluster parameters. Gaia-ESO Survey data for 167 potential members have yielded radial velocity measurements, which were used to determine the systemic velocity of the cluster and membership of individual stars. Atmospheric parameters were also used as a check on membership when available. Literature photometry was used to re-determine cluster parameters based on radial velocity member stars only; theoretical isochrones are fit in the V, V-I diagram. Cluster abundance measurements of ten radial-velocity member stars with high-resolution spectroscopy are presented for 24 elements. These abundances have been compared to local disk stars, and where possible placed within the context of literature gradient studies. We find Trumpler 23 to have an age of 0.80+/-0.10Gyr, significant differential reddening with an estimated mean cluster E(V-I) of 1.02^+0.14^_-0.09_, and an apparent distance modulus of 14.15+/-0.20. We find an average cluster metallicity of [Fe/H]=0.14+/-0.03dex, a solar [{alpha}/Fe] abundance, and notably subsolar [s-process/Fe] abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/447/921
- Title:
- Galactic Open Cluster Candidates
- Short Name:
- J/A+A/447/921
- Date:
- 14 Jan 2022 07:59:11
- Publisher:
- CDS
- Description:
- An inspection of DSS and 2MASS images of selected Milky Way regions led to the discovery of 66 stellar groupings whose morphologies, color-magnitude diagrams and stellar density distributions suggest that these objects are possible open clusters that are not yet listed in any catalogue. For 24 of these, which we consider to be the most likely candidates, we provide extensive descriptions on the basis of 2MASS photometry and their visual impression on DSS and 2MASS. Of those cluster candidates, 9 have fundamental parameters determined by fitting the color-magnitude diagrams with solar metallicity Padova isochrones. Additional 10 cluster candidates have distance moduli and reddenings derived from K magnitudes and (J-K) color indices of helium-burning red clump stars. As an addendum, we provide a list of a number of apparently yet unknown galactic and extragalactic objects which were also discovered during the survey.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A54
- Title:
- Galactic open clusters in RAVE
- Short Name:
- J/A+A/562/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ([M/H]). Here we provide and discuss newly obtained RV and [M/H] data, which will enable us to reinvestigate potential groupings of open clusters and associations.
- ID:
- ivo://CDS.VizieR/J/AJ/153/99
- Title:
- Galactic outer disk: a field toward Tombaugh 1
- Short Name:
- J/AJ/153/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We employ optical photometry and high-resolution spectroscopy to study a field toward the open cluster Tombaugh 1, where we identify a complex population mixture that we describe in terms of young and old Galactic thin disks. Of particular interest is the spatial distribution of the young population, which consists of dwarfs with spectral types as early as B6 and is distributed in a blue plume feature in the color-magnitude diagram. For the first time, we confirm spectroscopically that most of these stars are early-type stars and not blue stragglers or halo/thick-disk subdwarfs. Moreover, they are not evenly distributed along the line of sight but crowd at heliocentric distances between 6.6 and 8.2 kpc. We compare these results with present-day understanding of the spiral structure of the Galaxy and suggest that they trace the outer arm. This range of distances challenges current Galactic models adopting a disk cutoff at 14 kpc from the Galactic center. The young dwarfs overlap in space with an older component, which is identified as an old Galactic thin disk. Both young and old populations are confined in space since the disk is warped at the latitude and longitude of Tombaugh 1. The main effects of the warp are that the line of sight intersects the disk and entirely crosses it at the outer arm distance and that there are no traces of the closer Perseus arm, which would then be either unimportant in this sector or located much closer to the formal Galactic plane. Finally, we analyze a group of giant stars, which turn out to be located at very different distances and to possess very different chemical properties, with no obvious relation to the other populations.
