- ID:
- ivo://CDS.VizieR/J/ApJ/640/L43
- Title:
- Metallicities of RR Lyrae stars in Omega Cen
- Short Name:
- J/ApJ/640/L43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spectroscopic metal abundances for 74 RR Lyrae (RRL) stars in {omega} Cen obtained with FLAMES. The well-known metallicity spread is visible among the RRL variables. The metal-intermediate (MI) RRL stars ([Fe/H]~-1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H]~-1.7), in good agreement with the corresponding zero-age horizontal-branch models with cosmological helium abundance Y=0.246.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/653/L8
- Title:
- Metallicities on multiple MSs of Omega Centauri
- Short Name:
- J/A+A/653/L8
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Omega Cen is a rare example of a globular cluster where the iron abundance of the stars spans more than one order of magnitude. Many spectroscopic investigations of its red-giant- and sub-giant- branches have revealed multiple peaks in the iron abundance distribution. The metallicity distribution of main-sequence (MS) stars is not well characterized yet, due to the faintness of the stars and lack of data. So far, almost all studies of MS stars are based on photometric measurements. Our goal is to investigate the metallicity distribution of a statistically significant sample of MS stars in Omega Cen. In particular, we aim at revisiting the metallicity difference between the red and blue MS of the cluster. We use MUSE spectra obtained for the central region of omega Cen to derive metallicities for ~4200 MS stars. We find that blue MS stars are on average ~0.1dex more metal-rich than their red counterparts. On the basis of this new estimate, we find that the two sequences can be fit on the Hubble Space Telescope color-magnitude diagram with two isochrones having the same global metallicity and age but a higher helium abundance for the blue MS, i.e. {DELTA}Y~<0.1. Furthermore, we determine the average metallicity of the five main populations along Omega Cen MS and these estimates are consistent with expectations from previous photometric studies.
- ID:
- ivo://CDS.VizieR/J/A+A/508/1285
- Title:
- Metallicity estimates of M31 globular clusters
- Short Name:
- J/A+A/508/1285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new homogeneous set of metallicity estimates based on Lick indices for the old globular clusters of the M31 galaxy. The final aim is to add homogeneous spectroscopic metallicities to as many entries as possible of the Revised Bologna Catalog of M31 (www.bo.astro.it/M31) clusters, by reporting Lick index measurements from any source (literature, new observations, etc.) on the same scale.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A122
- Title:
- Metallicity of NGC 6388
- Short Name:
- J/A+A/659/A122
- Date:
- 15 Mar 2022 06:09:01
- Publisher:
- CDS
- Description:
- NGC 6388 is one of the most massive Galactic globular clusters (GC) and it is an old, metal-rich, Galactic bulge cluster. By exploiting previous spectroscopic observations we were able to bypass the uncertainties in membership related to the strong field stars contamination. We present the abundance analysis of 12 new giant stars with UVES spectra and 150 giants with GIRAFFE spectra acquired at the ESO-VLT. We derived radial velocities, atmospheric parameters and iron abundances for all stars. When combined to previous data, we obtain a grand total of 185 stars homogeneously analysed in NGC 6388 from high-resolution spectroscopy. The average radial velocity of the 185 stars is 81.2+/-0.7, rms=9.4km/s. We obtain an average metallicity [Fe/H]=-0.480dex, rms=0.045 dex (35 stars) and [Fe/H]=-0.488dex, rms=0.040dex (150 stars) from the UVES and GIRAFFE samples, respectively. Comparing these values to internal errors in abundance, we exclude the presence of a significant intrinsic metallicity spread within the cluster. Since about a third of giants in NGC 6388 is claimed to belong to the anomalous red giants in the HST pseudo-colour map defining the so-called type-II GCs, we conclude that either enhanced metallicity is not a necessary requisite to explain this classification (as also suggested by the null iron spread for NGC 362) or NGC 6388 is not a type-II globular cluster.
- ID:
- ivo://CDS.VizieR/J/MNRAS/396/1895
- Title:
- MgI and sTiO index definitions
- Short Name:
- J/MNRAS/396/1895
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the near-infrared spectral stellar library of Cenarro et al. (J/MNRAS/326/959), the behaviour of the MgI line at 8807{AA} and nearby TiO bands is analyzed in terms of the effective temperature, surface gravity and metallicity of the library stars. New spectroscopic indices for both spectral features - namely MgI and sTiO - are defined, and their sensitivities to different signal-to-noise ratios, spectral resolutions, flux calibrations and sky emission-line residuals are characterized. The two new indices exhibit interesting properties. In particular, MgI is a good indicator of the Mg abundance, whereas sTiO is a powerful dwarf-to-giant discriminator for cold spectral types. Empirical fitting polynomials that reproduce the strength of the new indices as a function of the stellar atmospheric parameters are computed, and a fortran routine with the fitting function predictions is made available. A thorough study of several error sources, non-solar [Mg/Fe] ratios and their influence on the fitting function residuals is also presented. From this analysis, an [Mg/Fe] underabundance of ~-0.04 is derived for the Galactic open cluster M67.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/820
- Title:
- M87 globular cluster candidates catalog
- Short Name:
- J/MNRAS/455/820
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new photometric catalogue of the rich globular cluster (GC) system around M87, the brightest cluster galaxy in Virgo. Using archival Next Generation Virgo Cluster Survey images in the ugriz bands, observed with Canada-France-Hawaii Telescope/MegaPrime, we perform a careful subtraction of the galaxy's halo light in order to detect objects at small galactocentric radii as well as in the wider field, and find 17620 GC candidates over a radius range from 1.3 to 445kpc with g<24mag. By inferring their colour, radial and magnitude distributions in a Bayesian way, we find that they are well described as a mixture of two GC populations and two distinct contaminant populations, but confirm earlier findings of radius-dependent colour gradients in both GC populations. This is consistent with a picture in which the more enriched GCs reside deeper in the galaxy's potential well, indicating a role for dissipative collapse in the formation of both the red and the blue GCs.
- ID:
- ivo://CDS.VizieR/J/ApJS/73/671
- Title:
- M87 globular clusters BVI photometry
- Short Name:
- J/ApJS/73/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry in B, V, and I for a sample of globular clusters in the Virgo central giant elliptical galaxy M87. Our measured sample comprises 270 objects brighter than V~23.4mag and with distances r>25" (>2kpc) from the center of the galaxy. In agreement with the recent study of Cohen, we find no detectable gradient of mean cluster color (metallicity) in (B-V) or (V-I) with radial distance. The cluster system does, however, display a large dispersion in color at any radius, corresponding to sigma([Fe/H])~0.6 about a mean metallicity (Fe/H]>~-1.1 according to our color index scale. The difference in mean color between the globular clusters and the underlying halo light of the galaxy itself, found previously by Strom and coworkers and by Cohen, shows up strongly in all of our color indices; we find virtually no clusters as red as mean color of the halo stars at any radius.
- ID:
- ivo://CDS.VizieR/J/AJ/122/2458
- Title:
- M31 globular clusters from HST
- Short Name:
- J/AJ/122/2458
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters at the distance of M31 have apparent angular sizes of a few arcseconds. While many M31 globular clusters have been detected and studied from ground-based images, the high spatial resolution of the Hubble Space Telescope (HST) allows much more robust detection and characterization of star cluster properties. We present the results of a search of 157 HST Wide Field Planetary Camera 2 images of M31. We found 82 previously catalogued globular cluster candidates, as well as 32 new globular cluster candidates and 20 open cluster candidates. We present images of the new candidates and photometry for all clusters. We assess existing cluster catalogs' completeness and use the results to estimate the total number of globular clusters in M31 as 460+/-70. The specific frequency is S_N_=1.2+/-0.2 and the mass specific frequency T=2.4+/-0.4; these values are at the upper end of the range seen for spiral galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/119/727
- Title:
- M31 globular clusters photometry
- Short Name:
- J/AJ/119/727
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of photometric and spectroscopic data on M31 globular clusters (GCs). The catalog includes new optical and near-infrared photometry for a substantial fraction of the 435 clusters and cluster candidates. We use these data to determine the reddening and intrinsic colors of individual clusters, and we find that the extinction laws in the Galaxy and M31 are not significantly different. There are significant (up to 0.2 mag in V-K) offsets between the clusters' intrinsic colors and simple stellar population colors predicted by population synthesis models; we suggest that these are due to systematic errors in the models. The distributions of M31 clusters' metallicities and metallicity-sensitive colors are bimodal, with peaks at [Fe/H]~-1.4 and -0.6. The distribution of V-I is often bimodal in elliptical galaxies' globular cluster systems, but it is not sensitive enough to metallicity to show bimodality in M31 and Galactic cluster systems. The radial distribution and kinematics of the two M31 metallicity groups imply that they are analogs of the Galactic "halo" and "disk/bulge" cluster systems. The globular clusters in M31 have a small radial metallicity gradient, suggesting that some dissipation occurred during the formation of the globular cluster system. The lack of correlation between cluster luminosity and metallicity in M31 GCs shows that self-enrichment is not important in GC formation.
- ID:
- ivo://CDS.VizieR/J/AJ/133/2764
- Title:
- M31 globular clusters structural parameters
- Short Name:
- J/AJ/133/2764
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The structures of globular clusters (GCs) reflect their dynamical states and past histories. High-resolution imaging allows the exploration of morphologies of clusters in other galaxies. Surface brightness profiles from new Hubble Space Telescope observations of 34 GCs in M31 are presented, together with fits of several different structural models to each cluster. M31 clusters appear to be adequately fit by standard King models and do not obviously require alternate descriptions with relatively stronger halos, such as are needed to fit many GCs in other nearby galaxies. The derived structural parameters are combined with corrected versions of those measured in an earlier survey in order to construct a comprehensive catalog of structural and dynamical parameters for M31 GCs with a sample size similar to that for the Milky Way. Clusters in M31, the Milky Way, Magellanic Clouds, the Fornax dwarf spheroidal, and NGC 5128 define a very tight fundamental plane with identical slopes. The combined evidence for these widely different galaxies strongly reinforces the view that old GCs have near-universal structural properties, regardless of host environment.
