scholarly journals The vertical Na–O relation in the bulge globular cluster NGC 6553

2020 ◽  
Vol 492 (3) ◽  
pp. 3742-3752 ◽  
Author(s):  
C Muñoz ◽  
S Villanova ◽  
D Geisler ◽  
C C Cortés ◽  
C Moni Bidin ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Globular Clusters ◽  
High Resolution Spectroscopy ◽  
Homogeneous Distribution ◽  
Light Elements ◽  
Chemical Abundance ◽  
Origin And Evolution ◽  
Red Giant ◽  
Vertical Relation ◽  
Detailed Chemical

ABSTRACT In this article, we present a detailed chemical analysis of seven red giant members of NGC 6553 using high-resolution spectroscopy from VLT FLAMES. We obtained the stellar parameters (Teff, Log(g), vt, [Fe/H]) of these stars from the spectra, and we measured the chemical abundance for 20 elements, including light elements, iron-peak elements, α-elements, and neutron-capture elements. The metallicities in our sample stars are consistent with a homogeneous distribution. We found a mean of [Fe/H] = −0.14 ± 0.07 dex, in agreement with other studies. Using the α-elements Mg, Si, Ca, and Ti, we obtain the mean of [α/Fe] = 0.11 ± 0.05. We found a vertical relation between Na and O, characterized by a significant spread in Na and an almost non-existent spread in O. In fact, Na and Al are the only two light elements with a large intrinsic spread, which demonstrates the presence of multiple populations (MPs). An intrinsic spread in Mg is not detected in this study. The α, iron-peak, and neutron-capture elements show good agreement with the trend of the bulge field stars, indicating similar origin and evolution, in concordance with our previous studies for two other bulge globular clusters (NGC 6440 and NGC 6528).

scholarly journals Chemical abundances of multiple stellar populations in massive globular clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 267-274 ◽  
Author(s):  
Anna F. Marino
Keyword(s):  
Neutron Capture ◽  
Globular Clusters ◽  
Milky Way ◽  
Stellar Populations ◽  
Slow Neutron ◽  
Light Elements ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Origin And Evolution

AbstractMultiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.

scholarly journals Chemical analysis of NGC 6528: one of the most metal-rich bulge globular clusters

2018 ◽  
Vol 620 ◽  
pp. A96 ◽  
Author(s):  
C. Muñoz ◽  
D. Geisler ◽  
S. Villanova ◽  
I. Saviane ◽  
C. C. Cortés ◽  
...  
Keyword(s):  
High Resolution ◽  
Chemical Analysis ◽  
Iron Content ◽  
Globular Clusters ◽  
Chemical Characterization ◽  
Heavy Elements ◽  
High Resolution Spectroscopy ◽  
Origin And Evolution ◽  
Red Giant ◽  
Good Agreement

Context. The bulge globular clusters (GCs) are key tracers of the bulge, a central and ancient component of our Galaxy. It is essential to understand their formation and evolution to study that of the bulge, as well as their relationship with the other Galactic GC systems (halo and disk GCs). High-resolution spectroscopy is a powerful tool for such studies, allowing us to obtain a detailed chemical characterization and kinematics of the clusters and to compare their chemical patterns with those of their halo and disk counterparts. Aims. Our main goals are to obtain detailed abundances for a sample of seven red giant members of NGC 6528 in order to characterize their chemical composition and study the relationship of this GC with the bulge, and with other bulge, halo, and disk GCs. Moreover, we analyze this cluster’s behavior associated with the multiple-populations phenomenon. Methods. We obtained the stellar parameters and chemical abundances of light elements (Na, Al), iron-peak elements (V, Cr, Mn, Fe, Co, Ni, Cu), α-elements (O, Mg, Si, Ca, Ti) and heavy elements (Zr, Ba, Eu) in seven red giant members of NGC 6528 using high-resolution spectroscopy from FLAMES-UVES. Results. In six stars of our sample we obtained a mean iron content of [Fe/H] = − 0.14 ± 0.03 dex, in good agreement with other studies. We found no significant internal iron spread. We detected one candidate variable star, which was excluded from the mean in iron content, and derived a metallicity in this star of [Fe/H] = − 0.55 ± 0.04 dex. Moreover, we found no extended O-Na anticorrelation but instead only an intrinsic Na spread. In addition, NGC 6528 does not exhibit a Mg-Al anticorrelation, and no significant spread in either Mg or Al. The α and iron-peak elements show good agreement with the bulge field star trend. The heavy elements are slightly dominated by the r-process. The chemical analysis suggests an origin and evolution similar to that of typical old Galactic bulge field stars. Finally, we find remarkable agreement in the chemical patterns of NGC 6528 and another bulge GC, NGC 6553, suggesting a similar origin and evolution.

scholarly journals Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

2017 ◽  
Vol 609 ◽  
pp. A13 ◽  
Author(s):  
Andreas Koch ◽  
Terese T. Hansen ◽  
Andrea Kunder
Keyword(s):  
Globular Clusters ◽  
Open Cluster ◽  
Light Element ◽  
Thick Disk ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Low Mass ◽  
Red Giant ◽  
Significant Spread ◽  
Detailed Chemical

Star clusters, particularly those objects in the disk-bulge-halo interface are as yet poorly charted, despite the fact that they carry important information about the formation and the structure of the Milky Way. Here, we present a detailed chemical abundance study of the recently discovered object Gaia 1. Photometry has previously suggested it as an intermediate-age, moderately metal-rich system, although the exact values for its age and metallicity remained ambiguous in the literature. We measured detailed chemical abundances of 14 elements in four red giant members, from high-resolution (R = 25 000) spectra that firmly establish Gaia 1 as an object associated with the thick disk. The resulting mean Fe abundance is −0.62 ± 0.03(stat.)± 0.10(sys.) dex, which is more metal-poor than indicated by previous spectroscopy from the literature, but it is fully in line with values from isochrone fitting. We find that Gaia 1 is moderately enhanced in the α-elements, which allowed us to consolidate its membership with the thick disk via chemical tagging. The cluster’s Fe-peak and neutron-capture elements are similar to those found across the metal-rich disks, where the latter indicate some level of s-process activity. No significant spread in iron nor in other heavy elements was detected, whereas we find evidence of light-element variations in Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations, typically seen in old globular clusters, are not seen in our data. This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1’s present-day membership with the thick disk, even though it remains unclear which mechanisms put it in that place.

scholarly journals IC 4499 revised: Spectro-photometric evidence of small light-element variations

2018 ◽  
Vol 618 ◽  
pp. A131 ◽  
Author(s):  
E. Dalessandro ◽  
C. Lardo ◽  
M. Cadelano ◽  
S. Saracino ◽  
N. Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Light Element ◽  
High Resolution Spectroscopy ◽  
Multiple Populations ◽  
Number Ratio ◽  
Red Giant ◽  
Good Agreement

It has been suggested that IC 4499 is one of the very few old globulars to not host multiple populations with light-element variations. To follow-up on this very interesting result, here we have made use of accurate HST photometry and FLAMES at VLT high-resolution spectroscopy to investigate in more detail the stellar population properties of this system. We find that the red giant branch of the cluster is clearly bimodal in near-UV-optical colour-magnitude diagrams, thus suggesting that IC 4499 is actually composed by two sub-populations of stars with different nitrogen abundances. This represents the first detection of multiple populations in IC 4499. Consistently, we also find that one star out of six is Na-rich to some extent, while we do not detect any evidence of intrinsic spread in both Mg and O. The number ratio between stars with normal and enriched nitrogen is in good agreement with the number ratio – mass trend observed in Galactic globular clusters. Also, as typically found in other systems, nitrogen rich stars are more centrally concentrated than normal stars, although this result cannot be considered conclusive because of the limited field of view covered by our observations (∼1rh). On the contrary, we observe that both the RGB UV colour spread, which is a proxy of N variations, and Na abundance variations, are significantly smaller than those observed in Milky Way globular clusters with mass and metallicity comparable to IC 4499. The modest N and Na spreads observed in this system can be tentatively connected to the fact that IC 4499 likely formed in a disrupted dwarf galaxy orbiting the Milky Way, as previously proposed based on its orbit.

The role of AGB stars in the evolution of globular clusters

2018 ◽  
Vol 14 (S343) ◽  
pp. 291-300
Author(s):  
Paolo Ventura ◽  
Franca D’Antona ◽  
Marcella Di Criscienzo ◽  
Flavia Dell’Agli ◽  
Marco Tailo
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Globular Clusters ◽  
State Of The Art ◽  
High Resolution Spectroscopy ◽  
Agb Stars ◽  
Light Elements ◽  
Original Population ◽  
Traditional Paradigm

AbstractThe results from high-resolution spectroscopy and accurate photometry have challenged the traditional paradigm that stars in globular clusters (GC) are simple stellar populations, rather suggesting that these structures harbor distinct groups of stars, differing in the chemical composition, particularly in the abundances of the light elements, from helium to silicon. Because this behavior is not shared by field stars, it is generally believed that some self-enrichment mechanism must have acted in GC, such that new stellar generations formed from the ashes of stars belonging to the original population. In this review, after presenting the state-of-the-art of the observations of GC stars, we discuss the possibility that the pollution of the intra-cluster medium was provided by the winds of AGB stars of initial mass above ∼3 M⊙. These objects evolve with time scales of 40 − 100 Myr and contaminate their surroundings with gas processed by p-capture nucleosynthesis, in agreement with the chemical patterns traced by GC stars.

scholarly journals A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

2019 ◽  
Vol 631 ◽  
pp. A14 ◽  
Author(s):  
M. Latour ◽  
T.-O. Husser ◽  
B. Giesers ◽  
S. Kamann ◽  
F. Göttgens ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Signal To Noise Ratio ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Multiple Populations ◽  
Synthetic Populations ◽  
Central Regions ◽  
Chromosome Maps ◽  
Red Giant

Context. Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as “chromosome maps”. These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both only available for a limited number of stars. Aims. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1115 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. Methods. We used the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combined the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Results. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808. Conclusions. We demonstrate that in spite of their low resolution, the MUSE spectra can be used to investigate abundance variations in the context of multiple populations.

scholarly journals Chemical abundance analysis of red giant branch stars in the globular cluster E3

2018 ◽  
Vol 616 ◽  
pp. A181 ◽  
Author(s):  
L. Monaco ◽  
S. Villanova ◽  
G. Carraro ◽  
A. Mucciarelli ◽  
C. Moni Bidin
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Abundance Ratio ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Multiple Populations ◽  
Red Giant ◽  
A Minor ◽  
Giant Branch Stars

Context. Globular clusters are known to host multiple stellar populations, which are a signature of their formation process. The globular cluster E3 is one of the few low-mass globulars that is thought not to host multiple populations. Aims. We investigate red giant branch stars in E3 with the aim of providing a first detailed chemical inventory for this cluster, we determine its radial velocity, and we provide additional insights into the possible presence of multiple populations in this cluster. Methods. We obtained high-resolution FLAMES-UVES/VLT spectra of four red giant branch stars likely members of E3. We performed a local thermodynamic equilibrium abundance analysis based on one-dimensional plane parallel ATLAS9 model atmospheres. Abundances were derived from line equivalent widths or spectrum synthesis. Results. We measured abundances of Na and of iron peak (Fe, V, Cr, Ni, Mn), α(Mg, Si, Ca, Ti), and neutron capture elements (Y, Ba, Eu). The mean cluster heliocentric radial velocity, metallicity, and sodium abundance ratio are νhelio = 12.6 ± 0.4 km s−1(σ = 0.6 ± 0.2 km s−1), [Fe/H] = −0.89 ± 0.08 dex, and [Na/Fe] = 0.18 ± 0.07 dex, respectively. The low Na abundance with no appreciable spread is suggestive of a cluster dominated by first-generation stars in agreement with results based on lower resolution spectroscopy. The low number of stars observed does not allow us to rule out a minor population of second-generation stars. The observed chemical abundances are compatible with the trends observed in Milky Way stars.

scholarly journals Spectroscopy and Photometry of the Least Massive Type II Globular Clusters: NGC 1261 and NGC 6934*

2021 ◽  
Vol 923 (1) ◽  
pp. 22
Author(s):  
A. F. Marino ◽  
A. P. Milone ◽  
A. Renzini ◽  
D. Yong ◽  
M. Asplund ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Slow Neutron ◽  
Type I ◽  
Type Ii ◽  
Chemical Abundances ◽  
Red Giant ◽  
First Time ◽  
Massive Clusters

Abstract Recent work has revealed two classes of globular clusters (GCs), dubbed Type I and Type II. Type II GCs are characterized by both a blue and a red red giant branch composed of stars with different metallicities, often coupled with distinct abundances in the slow neutron-capture elements (s-elements). Here we continue the chemical tagging of Type II GCs by adding the two least massive clusters of this class, NGC 1261 and NGC 6934. Based on both spectroscopy and photometry, we find red stars in NGC 1261 to be slightly enhanced in [Fe/H] by ∼0.1 dex and confirm that red stars of NGC 6934 are enhanced in iron by ∼0.2 dex. Neither NGC 1261 nor NGC 6934 show internal variations in the s-elements, which suggests a GC mass threshold for the occurrence of s-process enrichment. We found a significant correlation between the additional Fe locked in the red stars of Type II GCs and the present-day mass of the cluster. Nevertheless, most Type II GCs retained a small fraction of Fe produced by SNe II, lower than the 2%; NGC 6273, M54, and ω Centauri are remarkable exceptions. In the Appendix, we infer for the first time chemical abundances of lanthanum, assumed as representative of the s-elements, in M54, the GC located in the nucleus of the Sagittarius dwarf galaxy. Red-sequence stars are marginally enhanced in [La/Fe] by 0.10 ± 0.06 dex, in contrast with the large [La/Fe] spread of most Type II GCs. We suggest that different processes are responsible for the enrichment in iron and s-elements in Type II GCs.

scholarly journals HERBS II: Detailed chemical compositions of Galactic bulge stars

2019 ◽  
Vol 486 (4) ◽  
pp. 5349-5361 ◽  
Author(s):  
L Duong ◽  
M Asplund ◽  
D M Nataf ◽  
K C Freeman ◽  
M Ness
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Abundance Ratio ◽  
Chemical Compositions ◽  
Core Collapse ◽  
Detailed Chemistry ◽  
Red Clump ◽  
Red Giant ◽  
R Process ◽  
Detailed Chemical

ABSTRACT This work explores the detailed chemistry of the Milky Way bulge using the HERMES spectrograph on the Anglo-Australian Telescope. Here, we present the abundance ratios of 13 elements for 832 red giant branch and clump stars along the minor bulge axis at latitudes b = −10○, − 7.5○, and −5○. Our results show that none of the abundance ratios vary significantly with latitude. We also observe disc-like [Na/Fe] abundance ratios, which indicate that the bulge does not contain helium-enhanced populations as observed in some globular clusters. Helium enhancement is therefore not the likely explanation for the double red-clump observed in the bulge. We confirm that bulge stars mostly follow abundance trends observed in the disc. However, this similarity is not confirmed across all elements and metallicity regimes. The more metal-poor bulge population at [Fe/H] ≲ − 0.8 is enhanced in the elements associated with core collapse supernovae (SNeII). In addition, the [La/Eu] abundance ratio suggests higher r-process contribution, and likely higher star formation in the bulge compared to the disc. This highlights the complex evolution in the bulge, which should be investigated further, both in terms of modelling; and with additional observations of the inner Galaxy.

scholarly journals Lithium in the Old Open Cluster NGC 2243

2000 ◽  
Vol 198 ◽  
pp. 293-298 ◽  
Author(s):  
V. Hill ◽  
L. Pasquini
Keyword(s):  
High Resolution ◽  
Globular Clusters ◽  
Open Cluster ◽  
Interesting Case ◽  
The Other ◽  
High Resolution Spectroscopy ◽  
Giant Star ◽  
Other Hand ◽  
Red Giant ◽  
The One

We report observations of lithium in a sample of 11 stars in the metal-poor open cluster NGC 2243, that were obtained from high-resolution spectroscopy at CASPEC (ESO 3.6m telescope). The targets are located at the turnoff region, plus one red giant star.NGC 2243 is one of the most metal-poor open cluster, almost as deficient as 47 Tuc, but substantially younger (∼4 Gyrs and [Fe/H]=-0.5 dex), which makes it a very interesting case to compare with more metal rich coeval clusters on the one hand, and old metal-rich globular clusters (47 Tuc) on the other hand. The preliminary Lithium abundances obtained are discussed in this framework.

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