- ID:
- ivo://CDS.VizieR/J/ApJ/824/73
- Title:
- Abundances of NGC 6362 member stars
- Short Name:
- J/ApJ/824/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster (GC) where first- and second-generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch (RGB) and the red horizontal branch (RHB)) were observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H]=-1.09+/-0.01dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectively, the bluest and the reddest RGBs detected in the color-magnitude diagrams including the U filter. The RGB is composed of a mixture of first- and second-generation stars in a similar proportion, while almost all the RHB stars belong to the first cluster generation. To date, NGC 6362 is the least massive GC where both the photometric and spectroscopic signatures of multiple populations have been detected.
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- ID:
- ivo://CDS.VizieR/J/A+A/490/625
- Title:
- Abundances of NGC 6121 red giants
- Short Name:
- J/A+A/490/625
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present abundance analysis based on high resolution spectra of 105 isolated red giant branch (RGB) stars in the Galactic Globular Cluster NGC 6121 (M4). The data have been collected with FLAMES+UVES, at the ESO/VLT@UT2 telescope. Spectroscopic data were coupled with high precision wide-field UBVI_C photometry from WFI@2.2m telescope and infrared JHK photometry from 2MASS. We derived an average [Fe/H]=-1.07+/-0.01, and an {alpha} enhancement of [{alpha}/Fe]=+0.39+/-0.05dex (internal errors). We confirm the presence of an extended Na-O anticorrelation, and find two distinct groups of stars with significantly different Na and O content. We find no evidence of a Mg-Al anticorrelation. By coupling our results with previous studies on the CN band strength, we find that the CN strong stars have higher Na and Al content and are more O depleted than the CN weak ones. The two groups of Na-rich, CN-strong and Na-poor, CN-weak stars populate two different regions along the RGB. In the U vs. U-B color magnitude diagram the RGB spread is present from the base of the RGB to the RGB-tip. Apparently, both spectroscopic and photometric results imply the presence of two stellar populations in M4. We briefly discuss the possible origin of these populations.
- ID:
- ivo://CDS.VizieR/J/A+A/490/777
- Title:
- Abundances of Population II stars in NGC 6397
- Short Name:
- J/A+A/490/777
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Evolutionary trends in the surface abundances of heavier elements have recently been identified in the globular cluster NGC 6397 ([Fe/H]=-2), indicating the operation of atomic diffusion in these stars. Such trends constitute important constraints for the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. We perform an independent check of the reality and size of abundance variations within this metal-poor globular cluster. Observational data covering a large stellar sample, located between the cluster turn-off point and the base of the red giant branch, are homogeneously analysed. The spectroscopic data were obtained with the medium-high resolution spectrograph FLAMES/GIRAFFE on VLT-UT2 (R~27000). We derive independent effective-temperature scales from profile fitting of Balmer lines and by applying colour-Teff calibrations to Stroemgren uvby and broad-band BVI photometry. An automated spectral analysis code is used together with a grid of MARCS model atmospheres to derive stellar surface abundances of Mg, Ca, Ti, and Fe.
- ID:
- ivo://CDS.VizieR/J/AJ/149/153
- Title:
- Abundances of red giants in 10 globular clusters
- Short Name:
- J/AJ/149/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the light-element behavior of red giant stars in northern globular clusters (GCs) observed by the SDSS-III Apache Point Observatory Galactic Evolution Experiment. We derive abundances of 9 elements (Fe, C, N, O, Mg, Al, Si, Ca, and Ti) for 428 red giant stars in 10 GCs. The intrinsic abundance range relative to measurement errors is examined, and the well-known C-N and Mg-Al anticorrelations are explored using an extreme-deconvolution code for the first time in a consistent way. We find that Mg and Al drive the population membership in most clusters, except in M107 and M71, the two most metal-rich clusters in our study, where the grouping is most sensitive to N. We also find a diversity in the abundance distributions, with some clusters exhibiting clear abundance bimodalities (for example M3 and M53) while others show extended distributions. The spread of Al abundances increases significantly as cluster average metallicity decreases as previously found by other works, which we take as evidence that low metallicity, intermediate mass AGB polluters were more common in the more metal-poor clusters. The statistically significant correlation of [Al/Fe] with [Si/Fe] in M15 suggests that ^28^Si leakage has occurred in this cluster. We also present C, N, and O abundances for stars cooler than 4500K and examine the behavior of A(C+N+O) in each cluster as a function of temperature and [Al/Fe]. The scatter of A(C+N+O) is close to its estimated uncertainty in all clusters and independent of stellar temperature. A(C+N+O) exhibits small correlations and anticorrelations with [Al/Fe] in M3 and M13, but we cannot be certain about these relations given the size of our abundance uncertainties. Star-to-star variations of {alpha}-element (Si, Ca, Ti) abundances are comparable to our estimated errors in all clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/505/117
- Title:
- Abundances of red giants in 15 globular clusters
- Short Name:
- J/A+A/505/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present abundances of Fe, Na and O for 1409 red giant stars in 15 galactic globular clusters (GCs), derived from the homogeneous analysis of high resolution FLAMES/GIRAFFE spectra. The program clusters cover a range in metallicity from [Fe/H]=-2.4dex to [Fe/H]=-0.4dex, with a wide variety of global parameters (morphology of the horizontal branch, mass, concentration, etc.). For all clusters we find the Na-O anticorrelation, classical signature of the operation of proton-capture reactions in H burning at high temperature in a previous generation of more massive stars now extinct. Using quantitative criteria (from the morphology and extension of the Na-O anticorrelation), we can define three different components of the stellar population in GCs.
- ID:
- ivo://CDS.VizieR/J/A+A/505/139
- Title:
- Abundances of red giants in 17 globular clusters
- Short Name:
- J/A+A/505/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present homogeneous abundance determinations for iron and some of the elements involved in the proton-capture reactions (O, Na, Mg, Al, and Si) for 202 red giants in 17 Galactic globular clusters (GCs) from the analysis of high-resolution UVES spectra obtained with the FLAMES facility at the ESO VLT2 telescope. Our programme clusters span almost the whole range of the metallicity distribution of GCs and were selected to sample the widest range of global parameters (horizontal-branch morphology, masses, concentration, etc). In this paper we focus on the discussion of the Na-O and Mg-Al anticorrelations and related issues. Our study finds clear Na and O star-to-star abundance variations, exceeding those expected from the error in the analysis, in all clusters. Variations in Al are present in all but a few GCs. Finally, a spread in abundances of Mg and Si are also present in a few clusters. Mg is slightly less overabundant and Si slightly more overabundant in the most Al-rich stars.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A34
- Title:
- Abundances of red giants in M4 and 47 Tuc
- Short Name:
- J/A+A/550/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present aluminium abundances for a sample of about 100 red giant stars in each of the Galactic globular clusters 47 Tuc (NGC 104) and M 4 (NGC 6121). We have derived homogeneous abundances from intermediate-resolution FLAMES/GIRAFFE spectra. Aluminium abundances are from the strong doublet AlI 8772-8773{AA}, as in previous works done for giants in NGC 6752 and NGC 1851, and nitrogen abundances are extracted from a large number of features of the CN molecules by assuming a suitable carbon abundance. We added previous homogeneous abundances of O and Na and newly derived abundances of Mg and Si for our samples of 83 stars in M 4 and 116 stars in 47 Tuc to obtain the full set of elements from proton-capture reactions produced by different stellar generations in these clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/750/L14
- Title:
- Abundances of red giants in NGC 6752
- Short Name:
- J/ApJ/750/L14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present aluminum, magnesium, and silicon abundances in the metal-poor globular cluster NGC 6752 for a sample of more than 130 red giants with homogeneous oxygen and sodium abundances. We find that [Al/Fe] shows a spread of about 1.4 dex among giants in NGC 6752 and is anticorrelated with [Mg/Fe] and [O/Fe] and correlated with [Na/Fe] and [Si/Fe]. These relations are not continuous in nature, but the distribution of stars is clearly clustered around three distinct Al values, low, intermediate, and high. These three groups nicely correspond to the three distinct sequences previously detected using Stromgren photometry along the red giant branch. These two independent findings strongly indicate the existence of three distinct stellar populations in NGC 6752. Comparing the abundances of O and Mg, we find that the population with intermediate chemical abundances cannot originate from material with the same composition of the most O- and Mg-poor population, diluted by material with that of the most O- and Mg-rich one. This calls for different polluters.
- ID:
- ivo://CDS.VizieR/J/A+A/455/271
- Title:
- Abundances of red giants in NGC 6441
- Short Name:
- J/A+A/455/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of the present work is to determine accurate metallicities for a group of red giant branch stars in the field of the bulge Globular Cluster NGC 6441. This is the third paper in a series resulting from a large project aimed at determining the extent of the Na-O anticorrelation among Globular Cluster stars and exploring its relationship with HB morphology. We present an LTE abundance analysis of these objects, based on data gathered with the FLAMES fiber facility and the UVES spectrograph at VLT2. Results. Five of the thirteen stars observed are members of the cluster. The average Fe abundance for these five stars is [Fe/H]=-0.39+/-0.04+/-0.05dex, where the first error bar includes the uncertainties related to star-to-star random errors, and the second one the systematic effects related to the various assumptions made in the analysis.The overall abundance pattern is quite typical of Globular Clusters, with an excess of the alpha-elements and of Eu. There is evidence that the stars of NGC 6441 are enriched in Na and Al, while they have been depleted of O and Mg by H-burning at high temperatures, analogous with extensive observations of other Globular Clusters: in particular, one star is clearly Na and Al-rich and O and Mg-poor. We also obtained quite high V abundances, but it is possible that this is an artifact of the analysis, since similar high V abundances are also derived for the field stars. These last are all more metal-rich than NGC 6441 and probably belong to the bulge population bulge.
- ID:
- ivo://CDS.VizieR/J/A+A/464/967
- Title:
- Abundances of red giants in NGC 6388
- Short Name:
- J/A+A/464/967
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the LTE abundance analysis of high resolution spectra for red giant stars in the peculiar bulge globular cluster NGC 6388. Spectra of seven members were taken using the UVES spectrograph at the ESO VLT2 and the multiobject FLAMES facility. We exclude any intrinsic metallicity spread in this cluster: on average, [Fe/H]=-0.44+/-0.01+/-0.03dex on the scale of the present series of papers, where the first error bar refers to individual star-to-star errors and the second is systematic, relative to the cluster. Elements involved in H-burning at high temperatures show large spreads, exceeding the estimated errors in the analysis. In particular, the pairs Na and O, Al and Mg are anticorrelated and Na and Al are correlated among the giants in NGC 6388, the typical pattern observed in all galactic globular clusters studied so far. Stars in NGC 6388 shows an excess of alpha-process elements, similar to the one found in the twin bulge cluster NGC 6441. Mn is found underabundant in NGC 6388, in agreement with the average abundance ratio shown by clusters of any metallicity. Abundances of neutron-capture elements are homogeneously distributed within NGC 6388; the [Eu/Fe] ratio stands above the value found in field stars of similar metallicity.
