- 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.
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Search Results
- 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/564/A133
- Title:
- Gaia FGK benchmark stars: metallicity
- Short Name:
- J/A+A/564/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To calibrate automatic pipelines that determine atmospheric parameters of stars, one needs a sample of stars, or "benchmark stars", with well-defined parameters to be used as a reference. We provide detailed documentation of the iron abundance determination of the 34 FGK-type benchmark stars that are selected to be the pillars for calibration of the one billion Gaia stars. They cover a wide range of temperatures, surface gravities, and metallicities.
- ID:
- ivo://CDS.VizieR/III/281
- Title:
- Gaia FGK benchmark stars v2.1
- Short Name:
- III/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this era of large spectroscopic surveys of stars of the Milky Way, pipelines need to be tested and validated against a set of well-known stars. The Gaia FGK benchmark stars (GBS) are among the preferred samples of reference stars. They consist of a small but carefully selected sample of stars whose parameters are derived consistently and homogeneously. A series of papers has been published that discuss the definition and evolution of the sample of GBS. Here we summarise this work and provide our current list of stars with associated parameters which are recommended for validation and calibration purposes for stellar surveys.
- ID:
- ivo://CDS.VizieR/J/MNRAS/497/130
- Title:
- Gaia white dwarfs within 40pc. I
- Short Name:
- J/MNRAS/497/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic survey of 230 white dwarf candidates within 40pc of the Sun from the William Herschel Telescope and Gran Telescopio Canarias. All candidates were selected from Gaia Data Release 2 (DR2) and in almost all cases, had no prior spectroscopic classifications. We find a total of 191 confirmed white dwarfs and 39 main-sequence star contaminants. The majority of stellar remnants in the sample are relatively cool (<Teff>=6200K), showing either hydrogen Balmer lines or a featureless spectrum, corresponding to 89 DA and 76 DC white dwarfs, respectively. We also recover two DBA white dwarfs and 9-10 magnetic remnants. We find two carbon-bearing DQ stars and 14 new metal-rich white dwarfs. This includes the possible detection of the first ultra-cool white dwarf with metal lines. We describe three DZ stars for which we find at least four different metal species, including one that is strongly Fe- and Ni-rich, indicative of the accretion of a planetesimal with core-Earth composition. We find one extremely massive (1.31+/-0.01M_{sun}_) DA white dwarf showing weak Balmer lines, possibly indicating stellar magnetism. Another white dwarf shows strong Balmer line emission but no infrared excess, suggesting a low-mass sub-stellar companion. A high spectroscopic completeness (>99 per cent) has now been reached for Gaia DR2 sources within 40-pc sample, in the Northern hemisphere ({delta}>0{deg} and located on the white dwarf cooling track in the Hertzsprung-Russell diagram. A statistical study of the full northern sample is presented in a companion paper (McCleery et al., Paper II, 2020MNRAS.499.1890M, Cat. J/MNRAS/499/1890).
- ID:
- ivo://CDS.VizieR/J/A+A/289/740
- Title:
- Galactic abundance gradients
- Short Name:
- J/A+A/289/740
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/887/82
- Title:
- Galactic carbon stars infrared spectroscopy
- Short Name:
- J/ApJ/887/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal strong connections between stellar pulsations and the dust and molecular chemistry in their circumstellar shells. A sharp boundary in overall dust content, which predominantly measures the amount of amorphous carbon, separates the semiregular and Mira variables, with the semiregulars showing little dust in their spectra and the Miras showing more. In semiregulars, the contribution from SiC dust increases rapidly as the overall dust content grows, but in Miras, the SiC dust feature grows weaker as more dust is added. A similar dichotomy is found with the absorption band from CS at ~7.3{mu}m, which is generally limited to semiregular variables. Observationally, these differences make it straightforward to distinguish semiregular and Mira variables spectroscopically without the need for long-term photometric observations or knowledge of their distances. The rapid onset of strong SiC emission in Galactic carbon stars in semiregular variables points to a different dust-condensation process before strong pulsations take over. The break in the production of amorphous carbon between semiregulars and Miras seen in the Galactic sample is also evident in Magellanic carbon stars, linking strong pulsations in carbon stars to the strong mass-loss rates which will end their lives as stars across a wide range of metallicities.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A44
- Title:
- Galactic center CO rot-vib absorption lines
- Short Name:
- J/A+A/626/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the near- to mid-infrared wavelength domain, bright continuum sources in the central parsec of the Galactic center (GC) are subject to foreground absorption. These sources therefore represent ideal probes of the intervening material that is responsible for the absorption along the line of sight. Our aim is to shed light on the location and physics of the absorbing clouds. We try to find out which of the gaseous absorbing materials is intimately associated with the GC and which one is associated with clouds at a much larger distance. We used the capabilities of CRIRES spectrograph located at ESO Very Large Telescope in Chile to obtain absorption spectra of individual lines at a high spectral resolution of R=65000, that is, 5km/s. We observed the 12CO R(0), P(1), P(2), P(3), P(4), P(5), P(6), P(7) and P(9) transition lines, applied standard data reduction, and compared the results with literature data. Results. We present the results of CRIRES observations of 13 infrared sources located in the central parsec of the Galaxy. The data provide direct evidence for a complex structure of the interstellar medium along the line of sight and in the close environment of the central sources. In particular we find four cold foreground clouds at radial velocities vLS R of the order of -145, -85, -60, and -40+\/-15km/s that show absorption in the lower transition lines from R(0) to P(2) and in all the observed spectra.We also find in all sources an absorption in velocity range of 50-60km/s, possibly associated with the so-called 50km/s cloud and suggesting an extension of this cloud in front of the GC. Finally, we detect individual absorption lines that are probably associated with material much closer to the center and with the sources themselves, suggesting the presence of cold gas in the local region.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A141
- Title:
- Galactic center early-type stars catalog
- Short Name:
- J/A+A/585/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is still unclear whether the Sagittarius spiral arm is a major spiral arm in the Galaxy or whether it just outlines a region of enhanced star formation because of the local compression of gas. The best way to separate these scenarios out is to study the kinematics across the arm to determine the velocity perturbation it induces. A survey of early-type stars in the direction of the Galactic center is performed covering an area of 100 sq. deg with the aim of identifying candidates for a radial velocity study. Objective prism plates were obtained with the 4{deg} prism on the ESO Schmidt telescope using IIaO, 4415, and IIIaJ emulsions. The plates were digitized and more than 100k spectra were extracted down to a limiting magnitude of B=15m. The spectra were cross-correlated with a template with Balmer lines, which yielded a candidate list of 12675 early-type stars. Magnitudes and equivalent widths of strong lines were calculated from the spectra, which allowed us to estimate the individual extinctions and distances for 11075 stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/50
- Title:
- Galactic halo with APOGEE. II. Abundances.
- Short Name:
- J/ApJ/852/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental abundances and kinematics, pointing to different chemical and star formation histories (SFHs). In the present work, we explore, over a broader range in metallicity (-2.2<[Fe/H]<+0.5), the two stellar populations detected in the first paper of this series from metal-poor stars in DR13 of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We aim to infer signatures of the initial mass function (IMF) and the SFH from the two {alpha}-to-iron versus iron abundance chemical trends for the most APOGEE-reliable {alpha}-elements (O, Mg, Si, and Ca). Using simple chemical-evolution models, we infer the upper mass limit (Mup) for the IMF and the star formation rate, and its duration for each population. Compared with the low-{alpha} population, we obtain a more intense and longer-lived SFH, and a top-heavier IMF for the high-{alpha} population.
