| 1. |
- Pancino, E., et al.
(författare)
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The Gaia-ESO Survey : Calibration strategy
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 598
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Tidskriftsartikel (refereegranskat)abstract
- The Gaia-ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia. The calibration of GES is particularly delicate because of (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars; these targets have a large wide of metallicities and also include fast rotators, emission line objects, and stars affected by veiling; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the-art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4, which is the fourth internal GES data release and will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average off sets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals.
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| 2. |
- Jacobson, H. R., et al.
(författare)
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The Gaia-ESO Survey : Probes of the inner disk abundance gradient
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 591
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Tidskriftsartikel (refereegranskat)abstract
- Context. The nature of the metallicity gradient inside the solar circle (R-GC < 8 kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. Aims. 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. Methods. 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. Results. The GES open clusters exhibit a radial metallicity gradient of -0.10 +/- 0.02 dex kpc(-1), consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range R-GC similar to 6-12 kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. Conclusions. 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.
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| 3. |
- Lardo, C., et al.
(författare)
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The Gaia-ESO Survey: Kinematics of seven Galactic globular clusters
- 2015
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 573
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Tidskriftsartikel (refereegranskat)abstract
- The Gaia-ESO survey is a large public spectroscopic survey aimed at investigating the origin and formation history of our Galaxy by collecting spectroscopy of representative samples (about 105 Milky Way stars) of all Galactic stellar populations, in the field and in clusters. The survey uses globular clusters as intra-and inter-survey calibrators, deriving stellar atmospheric parameters and abundances of a significant number of stars in clusters, along with radial velocity determinations. We used precise radial velocities of a large number of stars in seven globular clusters (NGC 1851, NGC 2808, NGC 4372, NGC 4833, NGC 5927, NGC 6752, and NGC 7078) to validate pipeline results and to preliminarily investigate the cluster internal kinematics. Radial velocity measurements were extracted from FLAMES/GIRAFFE spectra processed by the survey pipeline as part of the second internal data release of data products to ESO. We complemented our sample with ESO archival data obtained with different instrument configurations. Reliable radial velocity measurements for 1513 bona fide cluster star members were obtained in total. We measured systemic rotation, estimated central velocity dispersions, and present velocity dispersion profiles of all the selected clusters, providing the first velocity dispersion curve and the first estimate of the central velocity dispersion for the cluster NGC 5927. Finally, we explore the possible link between cluster kinematics and other physical parameters. The analysis we present here demonstrates that Gaia-ESO survey data are sufficiently accurate to be used in studies of kinematics of stellar systems and stellar populations in the Milky Way.
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| 4. |
- Rojas-Arriagada, A., et al.
(författare)
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The Gaia-ESO Survey : Exploring the complex nature and origins of the Galactic bulge populations
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601
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Tidskriftsartikel (refereegranskat)abstract
- Context. As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge-and especially of the metal-poor bulge and their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data samples. Aims. We used the fourth internal data release of the Gaia-ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous sampling of the different Galactic populations provided by the Gaia-ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg /Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities. Methods. We obtained spectroscopic data for similar to 2500 red clump stars in 11 bulge fields, sampling the area -10 degrees <= l <= + 8 degrees and -10 degrees <= b <= -4 degrees from the fourth internal data release of the Gaia-ESO survey. A sample of similar to 6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a sample of stars likely located in the bulge region. Results. From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole sampled area. The relative ratio between the two modes of the MDF changes as a function of b, with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe] vs. [Fe/H] plane. On the other hand, metal-poor bulge stars have a more isotropic hot kinematics and do not participate in the X-shape bulge. Their Mg enhancement level and general shape in the [Mg/Fe] vs. [Fe/H] plane is comparable to that of the thick disk sequence. The position at which [Mg/Fe] starts to decrease with [Fe/H], called the "knee", is observed in the metal-poor bulge at [Fe/H] knee = -0.37 +/- 0.09, being 0.06 dex higher than that of the thick disk. Although this difference is inside the error bars, it suggest a higher star formation rate (SFR) for the bulge than for the thick disk. We estimate an upper limit for this difference of Delta [Fe/H](knee) = 0 : 24 dex. Finally, we present a chemical evolution model that suitably fits the whole bulge sequence by assuming a fast (< 1 Gyr) intense burst of stellar formation that takes place at early epochs. Conclusions. We associate metal-rich stars with the bar boxy/peanut bulge formed as the product of secular evolution of the early thin disk. On the other hand, the metal-poor subpopulation might be the product of an early prompt dissipative collapse dominated by massive stars. Nevertheless, our results do not allow us to firmly rule out the possibility that these stars come from the secular evolution of the early thick disk. This is the first time that an analysis of the bulge MDF and alpha-abundances has been performed in a large area on the basis of a homogeneous, fully spectroscopic analysis of high-resolution, high S/N data.
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| 5. |
- Thompson, B. B., et al.
(författare)
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The Gaia-ESO Survey : matching chemodynamical simulations to observations of the Milky Way
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 473:1, s. 185-197
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Tidskriftsartikel (refereegranskat)abstract
- The typical methodology for comparing simulated galaxies with observational surveys is usually to apply a spatial selection to the simulation to mimic the region of interest covered by a comparable observational survey sample. In this work, we compare this approach with a more sophisticated post-processing in which the observational uncertainties and selection effects (photometric, surface gravity and effective temperature) are taken into account. We compare a 'solar neighbourhood analogue' region in a model Milky Way-like galaxy simulated with RAMSES-CH with fourth release Gaia-ESO survey data. We find that a simple spatial cut alone is insufficient and that the observational uncertainties must be accounted for in the comparison. This is particularly true when the scale of uncertainty is large compared to the dynamic range of the data, e.g. in our comparison, the [Mg/Fe] distribution is affected much more than the more accurately determined [Fe/H] distribution. Despite clear differences in the underlying distributions of elemental abundances between simulation and observation, incorporating scatter to our simulation results to mimic observational uncertainty produces reasonable agreement. The quite complete nature of the Gaia-ESO survey means that the selection function has minimal impact on the distribution of observed age and metal abundances but this would become increasingly more important for surveys with narrower selection functions.
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| 6. |
- Thompson, B. B., et al.
(författare)
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The Gaia-ESO survey : Matching chemodynamical simulations to observations of the Milky Way
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 473:1, s. 185-197
-
Tidskriftsartikel (refereegranskat)abstract
- The typical methodology for comparing simulated galaxies with observational surveys is usually to apply a spatial selection to the simulation to mimic the region of interest covered by a comparable observational survey sample. In this work, we compare this approach with a more sophisticated post-processing in which the observational uncertainties and selection effects (photometric, surface gravity and effective temperature) are taken into account. We compare a 'solar neighbourhood analogue' region in a model MilkyWay-like galaxy simulated with RAMSES-CH with fourth release Gaia-ESO survey data. We find that a simple spatial cut alone is insufficient and that the observational uncertainties must be accounted for in the comparison. This is particularly true when the scale of uncertainty is large compared to the dynamic range of the data, e.g. in our comparison, the [Mg/Fe] distribution is affected much more than the more accurately determined [Fe/H] distribution. Despite clear differences in the underlying distributions of elemental abundances between simulation and observation, incorporating scatter to our simulation results to mimic observational uncertainty produces reasonable agreement. The quite complete nature of the Gaia-ESO survey means that the selection function has minimal impact on the distribution of observed age and metal abundances but this would become increasingly more important for surveys with narrower selection functions.
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| 7. |
- Fu, X., et al.
(författare)
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The Gaia-ESO Survey : Lithium enrichment histories of the Galactic thick and thin disc
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 610
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Tidskriftsartikel (refereegranskat)abstract
- Lithium abundance in most of the warm metal-poor main sequence stars shows a constarnt plateau (A(Li) similar to 2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium (ISM) at the solar system formation time, show a lithium abundance A(Li) similar to 3.26 dex. This pattern reflects the Li enrichment history of the ISM during the Galaxy lifetime. After the initial Li production in big bang nucleosynthesis, the sources of the enrichment include asymptotic giant branch (AGB) stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalogue and find a Li[alpha/Fe] anticorrelation independent of [Fe/H], T-eff, and log(g). Since in stellar evolution different alpha enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.
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