- ID:
- ivo://CDS.VizieR/J/AJ/131/1766
- Title:
- Abundances and equivalent widths in NGC 2808
- Short Name:
- J/AJ/131/1766
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the abundance analysis of stars from the tip of the red giant branch (RGB) to below the RGB bump in the globular cluster NGC 2808 based on high-resolution echelle spectra. We derive abundances of Al, {alpha}-process elements (SiI, CaI, TiI, and TiII), and Fe-group elements (ScII, VI, CrI, CrII, MnI, CoI, and NiI). Apart from Mg being somewhat reduced, likely because it has been depleted at the expense of Al in the MgAl cycle, the other {alpha}-element ratios show the overabundance typical of halo stars of similar metallicity.
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- ID:
- ivo://CDS.VizieR/J/AJ/120/1841
- Title:
- Abundances and Kinematics of Halo and Disk Stars
- Short Name:
- J/AJ/120/1841
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table gives the equivalent widths of the 168 stars used in the abundance analyses. For stars that may have multiple observations the mean value of the measurements is given for each line. Only lines used in the final abundance analysis are provided.
- ID:
- ivo://CDS.VizieR/J/A+A/416/1117
- Title:
- Abundances in the early Galaxy
- Short Name:
- J/A+A/416/1117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the framework of the ESO Large Programme "First Stars", very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (1992, Cat. <J/AJ/103/1987>, 1999, Cat. <J/AJ/117/981>), emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range -4.1<[Fe/H]<-2.7, and 22 stars have [Fe/H]<-3.0. Our new VLT/UVES spectra, at a resolving power of R~45000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (1995AJ....109.2757M) and Ryan et al. (1996ApJ...471..254R).
- ID:
- ivo://CDS.VizieR/J/A+A/579/A28
- Title:
- Abundances of 3 CEMP stars
- Short Name:
- J/A+A/579/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A170
- Title:
- Abundances of metal-poor stars
- Short Name:
- J/A+A/654/A170
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The study of old, metal-poor stars deepens our knowledge on the early stages of the universe. In particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their emission of ionising photons. We present a detailed chemical analysis and determination of the kinematic and orbital properties of a sample of 11 dwarf stars. These are metal-poor stars, and a few of them present a low lithium content. We inspected whether the other elements also present anomalies. We analysed the high-resolution UVES spectra of a few metal-poor stars using the Turbospectrum code to synthesise spectral lines profiles. This allowed us to derive a detailed chemical analysis of Fe, C, Li, Na, Mg, Al, Si, CaI, CaII, ScII, TiII, Cr, Mn, Co, Ni, Sr, and Ba. We find excellent coherence with the reference metal-poor First Stars sample. The lithium-poor stars do not present any anomaly of the abundance of the elements other than lithium. Among the Li-poor stars, we show that CS 22882-027 is very probably a blue-straggler. The star CS 30302-145, which has a Li abundance compatible with the plateau, has a very low Si abundance and a high Mn abundance. In many aspects, it is similar to the {alpha}-poor star HE 1424-0241, but it is less extreme. It could have been formed in a satellite galaxy and later been accreted by our Galaxy. This hypothesis is also supported by its kinematics.
- 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/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.
- ID:
- ivo://CDS.VizieR/J/A+A/464/939
- Title:
- Abundances of red giants in NGC 6218
- Short Name:
- J/A+A/464/939
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the multifiber spectrograph FLAMES on the ESO Very Large Telescope UT2 to derive atmospheric parameters, metallicities and abundances of O and Na for 79 red giant stars in the Galactic globular cluster NGC 6218 (M 12). We analyzed stars in the magnitude range from about 1mag below the bump to the tip of the Red Giant Branch. The average metallicity we derive is [Fe/H]=-1.31+/-0.004+/-0.028dex (random and systematic errors, respectively), with a very small star-to-star scatter (rms=0.033dex), from moderately high-resolution Giraffe spectra. This is the first extensive spectroscopic abundance analysis in this cluster. Our results indicate that NGC 6218 is very homogeneous as far as heavy elements are concerned. On the other hand, light elements involved in the well known proton-capture reactions of H-burning at high temperature, such as O and Na, show large variations, anticorrelated with each other, at all luminosities along the red giant branch. The conclusion is that the Na-O anticorrelation must be established in early times at the cluster formation. We interpret the variation of Na found near the RGB-bump as the effect of two distinct populations having different bump luminosities, as predicted for different He content. To our knowledge, NGC 6218 is the first GC where such a signature has been spectroscopically detected, when combined with consistent and homogeneous data obtained for NGC 6752 to gain in statistical significance.
- ID:
- ivo://CDS.VizieR/J/A+A/464/953
- Title:
- Abundances of red giants in NGC 6441
- Short Name:
- J/A+A/464/953
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of FLAMES-Giraffe spectra for several bright giants in NGC 6441, to investigate the presence and extent of the Na-O anticorrelation in this anomalous globular cluster. The field of NGC 6441 is very crowded, with severe contamination by foreground (mainly bulge) field stars. Appropriate membership criteria were devised to identify a group of 25 likely cluster members among the about 130 stars observed. Combined with the UVES data obtained with the same observations (Gratton et al., 2006, Cat. <J/A+A/455/271>), high dispersion abundance analyses are now available for a total of 30 stars in NGC 6441, 29 of them having data for both O and Na. The spectra were analyzed by a standard line analysis procedure; care was taken to minimize the impact of the differential interstellar reddening throughout the cluster, and to extract reliable information from crowded, and moderately high S/N (30-70), moderately high resolution (R~23000) spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/464/927
- Title:
- Abundances of red giants in NGC 6752
- Short Name:
- J/A+A/464/927
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are studying the Na-O anticorrelation in several globular clusters of different Horizontal Branch (HB) morphology in order to derive a possible relation between (primordial) chemical inhomogeneities and morphological parameters of the cluster population. We used the multifiber spectrograph FLAMES on the ESO Very Large Telescope UT2 and derived atmospheric parameters and elemental abundances of Fe, O and Na for about 150 red giant stars in the Galactic globular cluster NGC 6752. The average metallicity we derive is [Fe/H]=-1.56, in agreement with other results from red giants, but lower than obtained for dwarfs or early subgiants. In NGC 6752 there is not much space for an intrinsic spread in metallicity: on average, the rms scatter in [Fe/H] is 0.037+/-0.003dex, while the scatter expected on the basis of the major error sources is 0.039+/-0.003dex. The distribution of stars along the Na-O anticorrelation is different to what was found in the first paper of this series for the globular cluster NGC 2808: in NGC 6752 it is skewed toward more Na-poor stars, and it resembles more the one in M 13. Detailed modeling is required to clarify whether this difference may explain the very different distributions of stars along the HB.
