- ID:
- ivo://CDS.VizieR/J/A+AS/121/95
- Title:
- Giant stars abundances in 24 clusters
- Short Name:
- J/A+AS/121/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high resolution, high signal-to-noise ratio CCD echelle spectra of 10 bright red giants in 3 globular clusters (47 Tuc, NGC 6752 and NGC 6397) roughly spanning the whole range of metallicities of the galactic globular cluster system. The analysis of this newly acquired material reveals no significant evidence of star-to-star variation of the [Fe/H] ratio in these three clusters. Moreover, a large set of high quality literature data (equivalent widths from high dispersion CCD spectra) was re-analyzed in an homogeneous and self-consistent way to integrate our observations and derive new metal abundances for more than 160 bright red giants in 24 globular clusters (i.e. about 16% of the known population of galactic globulars). This set was then used to define a new metallicity scale for globular clusters which is the result of high quality, direct spectroscopic data, of new and updated model atmospheres from the grid of Kurucz (1992), and of a careful fine abundance analysis; this last, in turn, is based on a common set of both atomic and atmospheric parameters for all the stars examined.
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- ID:
- ivo://CDS.VizieR/J/A+A/584/A46
- Title:
- GIRAFFE Inner Bulge Survey (GIBS). II.
- Short Name:
- J/A+A/584/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate metallicity and {alpha}-element abundance gradients along a Galactic longitude strip, at latitude b~-4{deg}, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. High-resolution (R~22500) spectra for 400 Kgiants, in four fields within -4.8{deg}<~b<~-3.4{deg} and -10{deg}<~l<~+10{deg}, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ~400 stars in Baade's Window at (l,b)=(1{deg},-4{deg}), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions.
- ID:
- ivo://CDS.VizieR/J/ApJ/901/23
- Title:
- Gjoll stream stars & detailed abund. of 4 members
- Short Name:
- J/ApJ/901/23
- Date:
- 15 Feb 2022 14:07:06
- Publisher:
- CDS
- Description:
- Recent analysis of the second data release of Gaia has revealed a number of new stellar streams surrounding the Milky Way. It has been suggested that one of these streams, Gjoll, is associated with the globular cluster NGC 3201, but thus far the association has only been based on kinematics of the stream stars. In this work we identify five likely stream members in the Gaia data that are bright enough for high-resolution spectroscopic follow-up with the Harlan J. Smith telescope at McDonald Observatory. One star is ruled out as a member based on its radial velocity. Abundance analysis of the remaining four kinematic members reveals a good chemical match to NGC 3201 for two of the stars, driven by their similar Al and {alpha}-element abundances. Of the remaining two, one shows no chemical similarity to NGC 3201 and is likely an unassociated Milky Way halo field star, while the other exhibits a similar Al abundance but has somewhat lower {alpha}-element abundances. The chemical tagging of stars in the Gjoll stream to NGC3201 confirms this association and provides direct proof of the hierarchical formation of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A98
- Title:
- Globular cluster escapees in the Galactic halo
- Short Name:
- J/A+A/637/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A long-lasting open question in the field of Galactic archeology refers to the size of the contribution from former globular cluster (GC) stars to the formation of the stellar halo of the Milky Way. We contribute to answering this important question by establishing observational links between the present-day halo field star population and GCs. To this end, we combined astrometric information such as space motions and parallaxes from the second data release of the Gaia mission (Gaia DR2) with spectroscopic radial velocities and metallicities ([Fe/H]) from the Sloan Digital Sky Survey (SDSS-IV, DR14) to end up with a seven-dimensional chemodynamical information space for more than 3x10^5^ stars. Moreover, from our previous study, we incorporated the sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of globular cluster stellar populations. Using three different tagging techniques -- among which is the exploration of conservative integrals of motion -- we are able to establish unique associations between 151 extratidal stars in the neighborhood of eight GCs, which coincide with earlier findings of stellar envelopes beyond the tidal radius and even beyond (out to several tens of tidal radii). In addition, we trace the possible origin of about 62% of the sample of CN-strong giants to their potential host clusters. We find a connection between several of the involved GCs and the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we identify co- moving groups of stars at the same [Fe/H] with a possible cluster origin. Some of these associations contain RR Lyrae variables, which allows meaningful distance inferences to be made. From these, we find strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54, the massive cluster in Sagittarius' core remnant. Finally, by employing the counts of CN-strong and bona-fide CN-normal giants from our novel sample, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to 50.0+/-16.7% while the associations in the halo field rather imply 80.2-5.2+4.9%. We speculate that -- if proven real by spectroscopic follow-up -- the disparity between these numbers could indicate a major contribution of low- mass clusters to the overall number of stars escaped to the halo or could alternatively suggest strong mass loss from the first generation during early cluster dissolution.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A191
- Title:
- 885 globular cluster giants abundances
- Short Name:
- J/A+A/622/A191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to provide abundances of a large set of light and neutron-capture elements homogeneously analyzed that cover a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. We analyzed a large sample of 885 GCs giants from the SDSS~IV-Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We used the Cannon results to separate the red giant branch and asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) to derive metallicity, microturbulence, macroturbulence, many light-element abundances, and the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for low-metallicity GC stars. Furthermore, while we confirm most of the known correlations and anticorrelation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement. At the same time, these stars show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anticorrelation of the Al spread against clusters metallicity and luminosity, but the data do not allow us to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Large and homogeneously analyzed samples from ongoing spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anticorrelation, thus yielding new constrains for GCs formation/evolution models.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/5
- Title:
- Globular cluster intrinsic iron abundance spreads
- Short Name:
- J/ApJS/245/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an up-to-date catalog of intrinsic iron abundance spreads in the 55 Milky Way globular clusters (GCs) for which sufficiently precise spectroscopic measurements are available. Our method combines multiple data sets when possible to improve the statistics, taking into account the fact that different methods and instruments can lead to systematically offset metallicities. Only high spectral resolution (R>14000) studies that measure the equivalent widths of individual iron lines are found to have uncertainties on the metallicities of the individual stars that can be calibrated sufficiently well for the intrinsic dispersion to be separated cleanly from a random measurement error. The median intrinsic iron spread is found to be 0.045dex, which is small but unambiguously measured to be nonzero in most cases. There is large variation between clusters, but more luminous GCs, above 10^5^L_{sun}_, have increasingly large iron spreads on average; no trend between the iron spread and metallicity is found.
- ID:
- ivo://CDS.VizieR/J/AZh/96/267
- Title:
- Globular clusters abundances and kinematics
- Short Name:
- J/AZh/96/267
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- For the catalog, we compiled the abundances of 28 chemical elements: alpha-elements (O, Mg, Si, Ca, Ti), carbon, iron-peak elements(Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), slow and rapid neutron-capture elements (Sr, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, Dy) and three odd-Z elements(Na, Al, K) in the stars of 69 globular clusters. The data are taken from 101 papers published from 1986 to 2018. The abundances of chemical elements in stars of the clusters in almost all the used papers are determined from high-resolution spectra obtained mainly for the atmospheres of red giants. The spectra are analyzed with the local thermodynamic equilibrium approximation.
- ID:
- ivo://CDS.VizieR/J/A+A/296/680
- Title:
- Globular Clusters Djorg 1 and Pal 6
- Short Name:
- J/A+A/296/680
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present NTT V,I observations of Palomar 6 and Djorgovski 1, two obscured loose clusters in crowded fields. We derive a reddening of E(B-V)=1.33+/-0.10, a distance d_{sun}_=~8.9kpc, and a metallicity of [Fe/H]=~-0.4 for Pal 6, and E(B-V)=1.71+/-0.10, d_{sun}_=~8.8kpc, and a similar metallicity ([Fe/H]=~-0.4) for Djorg 1.
- ID:
- ivo://CDS.VizieR/J/ApJ/682/199
- Title:
- Globulars with X-ray sources in NGC 5128
- Short Name:
- J/ApJ/682/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We detect 353 X-ray point sources, mostly low-mass X-ray binaries (LMXBs), in four Chandra observations of Centaurus A (NGC 5128), the nearest giant early-type galaxy, and correlate this point-source population with the largest available ensemble of confirmed and likely globular clusters (GCs) associated with this galaxy. Of the X-ray sources, 31 are coincident with 30 GCs that are confirmed members of the galaxy by radial velocity measurement (two X-ray sources match one GC within our search radius), while one X-ray source coincides with a GC resolved by Hubble Space Telescope (HST) images. Another 36 X-ray point sources match probable, but spectroscopically unconfirmed, GC candidates.
- ID:
- ivo://CDS.VizieR/J/ApJ/527/879
- Title:
- Gravities for late-type stars
- Short Name:
- J/ApJ/527/879
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical analyses of late-type stars are usually carried out following the classical recipe: LTE line formation and homogeneous, plane-parallel, flux-constant, and LTE model atmospheres. We review different results in the literature that have suggested significant inconsistencies in the spectroscopic analyses, pointing out the difficulties in deriving independent estimates of the stellar fundamental parameters and hence, detecting systematic errors. The trigonometric parallaxes measured by the Hipparcos mission provide accurate appraisals of the stellar surface gravity for nearby stars, which are used here to check the gravities obtained from the photospheric iron ionization balance. We find an approximate agreement for stars in the metallicity range -1.0{<~}[Fe/H]{<~}0, but the comparison shows that the differences between the spectroscopic and trigonometric gravities decrease toward lower metallicities for more metal-deficient dwarfs (-2.5{<~}[Fe/H]{<~}-1.0), which casts a shadow upon the abundance analyses for extreme metal-poor stars that make use of the ionization equilibrium to constrain the gravity.