- ID:
- ivo://CDS.VizieR/J/A+A/592/A66
- Title:
- NGC 2808 AGB and RGB stars Na abundance
- Short Name:
- J/A+A/592/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic globular clusters (GC) are known to have multiple stellar populations and be characterised by similar chemical features, e.g., O-Na anti-correlation. While second-population stars, identified by their Na overabundance, have been found from the main sequence turnoff up to the tip of the red giant branch in various Galactic GCs, asymptotic giant branch stars have rarely been targeted. Here we present the results of our high-resolution spectroscopic study of a sample of AGB and RGB stars in the Galactic globular cluster NGC 2808. We derived accurate Na abundances for 31 AGB and 40 RGB stars in this cluster. Comparable Na abundance dispersions are found for our AGB and RGB samples, and we conclude that NGC 2808 has Na-rich second-population AGB stars, which turn out to be even more numerous - in relative terms - than their Na-poor counterparts (on the AGB) and the Na-rich stars on the RGB.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/607/A135
- Title:
- NGC 104, 6121 & 6809 AGB and RGB stars Na abundance
- Short Name:
- J/A+A/607/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze high-resolution spectra of a large sample of asymptotic giant branch AGB and red giant branch (RGB) stars in the Galactic GCs NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determine their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. We find that NGC 104 and NG 6809 have comparable AGB and RGB Na abundance distributions, while NGC 6121 shows a lack of very Na-rich AGB stars. Moreover, to investigate the dependence of AGB Na abundance dispersion on GC parameters, we compare the AGB [Na/H] distributions of a total of nine GCs, with five determined by ourselves with homogeneous method and four from literature, covering a wide range of GC parameters. Their Na abundances and multiple populations of AGB stars form complex picture. In some GCs, AGB stars have similar Na abundances and/or second-population fractions as their RGB counterparts, while some GCs do not have Na-rich second-population AGB stars, and various cases exist between the two extremes. In addition, the fitted relations between fractions of the AGB second population and GC global parameters show that the AGB second-population fraction slightly anticorrelates with GC central concentration, while no robust dependency can be confirmed with other GC parameters.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/39
- Title:
- NGC 6218 and NGC 5904 lithium abundances
- Short Name:
- J/ApJ/791/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Convergent lines of evidence suggest that globular clusters host multiple stellar populations. It appears that they experience at least two episodes of star formation whereby a fraction of first-generation stars contribute astrated ejecta to form the second generation(s). To identify the polluting progenitors, we require distinguishing chemical signatures such as that provided by lithium. Theoretical models predict that lithium can be synthesized in AGB stars, whereas no net Li production is expected from other candidates. It has been shown that in order to reproduce the abundance pattern found in M4, Li production must occur within the polluters, favoring the AGB scenario. Here, we present Li and Al abundances for a large sample of RGB stars in M12 and M5. These clusters have a very similar metallicity, while demonstrating differences in several cluster properties. Our results indicate that the first-generation and second-generation stars share the same Li content in M12; we recover an abundance pattern similar to that observed in M4. In M5, we find a higher degree of complexity, and a simple dilution model fails in reproducing the majority of the stellar population. In both clusters, we require Li production across the different stellar generations, but production seems to have occurred to different extents. We suggest that such a difference might be related to the cluster mass with the Li production being more efficient in less-massive clusters. This is the first time a statistically significant correlation between the Li spread within a GC and its luminosity has been demonstrated. Finally, although Li-producing polluters are required to account for the observed pattern, other mechanisms, such as MS depletion, might have played a role in contributing to the Li internal variation, though at a relatively low level.
- ID:
- ivo://CDS.VizieR/J/AJ/141/58
- Title:
- NGC 2204 and NGC 2243 red giant abundances
- Short Name:
- J/AJ/141/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed element abundances have been determined for 10-13 stars each in the open clusters (OCs) NGC 2204 and NGC 2243 based on Hydra multi-object echelle spectra obtained with the CTIO 4m telescope. We have found average cluster metallicities of [Fe/H]=-0.23+/-0.04 and -0.42+/-0.05 for NGC 2204 and NGC 2243, respectively, from an equivalent width analysis.
1225. NGC 6139 BV photometry
- ID:
- ivo://CDS.VizieR/J/A+A/583/A69
- Title:
- NGC 6139 BV photometry
- Short Name:
- J/A+A/583/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Information on globular clusters (GC) formation mechanisms can be gathered by studying the chemical signature of the multiple populations that compose these stellar systems. In particular, we investigate the anti-correlations among O, Na, Al, and Mg to explore the influence of cluster mass and environment on GCs in the Milky Way and in extragalactic systems. We present here the results obtained on NGC 6139, which, on the basis of its horizontal branch morphology, has been proposed to be dominated by first-generation stars. In our extensive study based on high-resolution spectroscopy, the first for this cluster, we found a metallicity of [Fe/H]=-1.579+/-0.015+/-0.058 (rms=0.040dex, 45 bona fide member stars) on the UVES scale defined by our group. The stars in NGC 6139 show a chemical pattern normal for GCs, with a rather extended Na-O (and Mg-Al) anticorrelation. NGC 6139 behaves as expected from its mass and contains a large portion (about two thirds) of second-generation stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/75
- Title:
- NGC 5824 giant star members from VLT obs.
- Short Name:
- J/ApJ/859/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 5824 is a massive Galactic globular cluster suspected to have an intrinsic spread in its iron content, according to the strength of the calcium triplet lines. We present chemical abundances of 117 cluster giant stars using high-resolution spectra acquired with the multi-object spectrograph FLAMES. The metallicity distribution of 87 red giant branch stars is peaked at [Fe/H]=-2.11+/-0.01dex, while that derived from 30 asymptotic giant branch stars is peaked at [Fe/H]=-2.20+/-0.01dex. Both the distributions are compatible with a null spread, indicating that this cluster did not retain the ejecta of supernovae. The small iron abundance offset between the two groups of stars is similar to the abundances already observed among red and asymptotic giant branch stars in other clusters. The lack of intrinsic iron spread rules out the possibility that NGC 5824 is the remnant of a disrupted dwarf galaxy, as previously suggested. We also find evidence of the chemical anomalies usually observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations. In particular, NGC 5824 exhibits a huge range of [Mg/Fe] abundance, observed in only a few metal-poor and/or massive clusters. We conclude that NGC 5824 is a normal globular cluster, without spread in [Fe/H] but with an unusually large spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by massive asymptotic giant branch stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/773/L36
- Title:
- NGC 5128 globular cluster abundances
- Short Name:
- J/ApJ/773/L36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present [Fe/H], ages, and Ca abundances for an initial sample of 10 globular clusters in NGC 5128 obtained from high-resolution, high signal-to-noise ratio echelle spectra of their integrated light. All abundances and ages are obtained using our original technique for high-resolution integrated light abundance analysis of globular clusters. The clusters have a range in [Fe/H] between -1.6 and -0.2. In this sample, the average [Ca/Fe] for clusters with [Fe/H]<-0.4 is +0.37+/-0.07, while the average [Ca/Fe] in our Milky Way (MW) and M31 GC samples is +0.29+/-0.09 and +0.24+/-0.10, respectively. This may imply a more rapid chemical enrichment history for NGC 5128 than for either the MW or M31. This sample provides the first quantitative picture of the chemical history of NGC 5128 that is directly comparable to what is available for the MW. Data presented here were obtained with the MIKE echelle spectrograph on the Magellan Clay Telescope.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/1609
- Title:
- NGC 2808 HB stars abundances
- Short Name:
- J/MNRAS/437/1609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an abundance analysis of 96 horizontal branch (HB) stars in NGC 2808, a globular cluster exhibiting a complex multiple stellar population pattern. These stars are distributed in different portions of the HB and cover a wide range of temperature. By studying the chemical abundances of this sample, we explore the connection between HB morphology and the chemical enrichment history of multiple stellar populations. For stars lying on the red HB, we use GIRAFFE and UVES spectra to determine Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y, Ba and Nd abundances. For colder, blue HB stars, we derive abundances for Na, primarily from GIRAFFE spectra. We were also able to measure direct non-local thermodynamic equilibrium He abundances for a subset of these blue HB stars with temperature higher than ~9000K. Our results show that: (i) HB stars in NGC 2808 show different content in Na depending on their position in the colour-magnitude diagram, with blue HB stars having higher Na than red HB stars; (ii) the red HB is not consistent with a uniform chemical abundance, with slightly warmer stars exhibiting a statistically significant higher Na content; and (iii) our subsample of blue HB stars with He abundances shows evidence of enhancement with respect to the predicted primordial He content by {Delta}Y=+0.09+/-0.01+/-0.05 (internal plus systematic uncertainty). Our results strongly support theoretical models that predict He enhancement among second-generation(s) stars in globular clusters and provide observational constraints on the second-parameter governing HB morphology.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A100
- Title:
- NGC 288 hot horizontal branch stars abundances
- Short Name:
- J/A+A/565/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 288 is a globular cluster with a well-developed blue horizontal branch covering the u-jump that indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. We compare observed abundances with predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition, we investigate the nature of the overluminous blue HB stars around the u-jump. We defined a new photometric index sz from uvby measurements that is gravity-sensitive between 8000K and 12000K. Using medium-resolution spectra and Stroemgren photometry, we determined atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We used both homogeneous and stratified model spectra for our spectroscopic analyses. The atmospheric parameters and masses of the hot HB stars in NGC 288 show a behaviour seen also in other clusters for temperatures between 9000K and 14000K. Outside this temperature range, however, they instead follow the results found for such stars in {omega} Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10^-7^M_{sun}_. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. When effective temperatures, surface gravities, and masses are determined with stratified model spectra, the hotter stars agree better with canonical evolutionary predictions. Our results show definite promise towards solving the long-standing problem of surface gravity and mass discrepancies for hot HB stars, but much work is still needed to arrive at a self-consistent solution.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A169
- Title:
- NGC 7009 MUSE imaging spectroscopic survey
- Short Name:
- J/A+A/620/A169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spatial structure of the emission lines and continuum over the 50-arcsecond extent of the nearby, O-rich, PN NGC 7009 (Saturn Nebula) have been observed with the MUSE integral field spectrograph on the ESO Very Large Telescope. This study concentrates on maps of line emission and their interpretation in terms of physical conditions. MUSE Science Verification data, in <0.6-arcsecond seeing, have been reduced and analysed as maps of emission lines and continuum over the wavelength range 4750-9350{AA}. The dust extinction, the electron densities and temperatures of various phases of the ionized gas, abundances of species from low to high ionization and some total abundances are determined using standard techniques. Emission line maps over the bright shells are presented, from neutral to the highest ionization available (HeII and [MnV]). For collisionally excited lines (CELs), maps of electron temperature (Te from [NII] and [SIII]) and density (Ne from [SII] and [ClIII]) are available and for optical recombination lines (ORLs) temperature (from the Paschen jump and ratio of HeI lines) and density (from high Paschen lines). These estimates are compared: for the first time, maps of the differences in CEL and ORL Te's have been derived, and correspondingly a map of t^2^ between a CEL and ORL temperature, showing considerable detail. Total abundances of only He and O were formed, the latter using three ionization correction factors. However the map of He/H is not flat, departing by ~2% from a constant value, with remnants corresponding to ionization structures. An integrated spectrum over an area of 2340-arcseconds squared was also formed and compared to 1D photoionization models. The spatial variation of a range of nebular parameters illustrates the complexity of the ionized media in NGC 7009. These MUSE data are very rich with detections of hundreds of lines over areas of hundreds of arcseconds squared and follow-on studies are outlined.
