scholarly journals An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13

2019 ◽  
Vol 632 ◽  
pp. A55 ◽  
Author(s):  
Andreas Koch ◽  
Patrick Côté
Keyword(s):  
Globular Cluster ◽  
Neutron Capture ◽  
Milky Way ◽  
Signal To Noise Ratio ◽  
Light Element ◽  
Chemical Abundance ◽  
Galactocentric Distance ◽  
The Mean ◽  
Remote System ◽  
Kinematic Properties

At a Galactocentric distance of 27 kpc, Palomar 13 is an old globular cluster (GC) belonging to the outer halo. We present a chemical abundance analysis of this remote system from high-resolution spectra obtained with the Keck/HIRES spectrograph. Owing to the low signal-to-noise ratio of the data, our analysis is based on a coaddition of the spectra of 18 member stars. We are able to determine integrated abundance ratios for 16 species of 14 elements, of α-elements (Mg, Si, Ca, and Ti), Fe-peak (Sc, Mn, Cr, Ni, Cu, and Zn), and neutron-capture elements (Y and Ba). While the mean Na abundance is found to be slightly enhanced and halo-like, our method does not allow us to probe an abundance spread that would be expected in this light element if multiple populations are present in Pal 13. We find a metal-poor mean metallicity of −1.91 ± 0.05 (statistical) ±0.22 (systematic), confirming that Pal 13 is a typical metal-poor representative of the outer halo. While there are some differences between individual α-elements, such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the mean [α/Fe] of 0.34 ± 0.06 is consistent with the marginally lower α component of the halo field and GC stars at similar metallicity. We discuss our results in the context of other objects in the outer halo and consider which of these objects were likely accreted. We also discuss the properties of their progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of its GCs, this is not supported by its kinematic properties within the Milky Way system. Moreover, its chemodynamical similarity with NGC 5466, a purported progeny of the Sequoia accretion event, might indicate a common origin in this progenitor. However, the ambiguities in the full abundance space of this comparison emphasize the difficulties in unequivocally labeling a single GC as an accreted object, let alone assigning it to a single progenitor.

scholarly journals The likelihood of undiscovered globular clusters in the outskirts of the Milky Way

2021 ◽  
Vol 502 (3) ◽  
pp. 4547-4557
Author(s):  
Jeremy J Webb ◽  
Raymond G Carlberg
Keyword(s):  
Equilibrium State ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Expected Number ◽  
Galactocentric Distance ◽  
Deep Imaging ◽  
Low Metallicity ◽  
Globular Cluster System ◽  
Kinematic Properties

ABSTRACT The currently known Galactic globular cluster population extends out to a maximum galactocentric distance of ∼145 kpc, with the peculiarity that the outermost clusters predominantly have an inward velocity. Orbit averaging finds that this configuration occurs by chance about $6{{\ \rm per\ cent}}$ of the time, suggesting that several globular clusters with positive radial velocities remain undiscovered. We evaluate the expected number of undiscovered clusters at large distances under the assumption that the cluster population has a smooth radial distribution and is in equilibrium within the Milky Way’s virial radius. By comparing the present day kinematic properties of outer clusters to random orbital configurations of the Galactic globular cluster system through orbit averaging, we estimate a likelihood of $73{{\ \rm per\ cent}}$ of there being at least one undiscovered globular cluster within the Milky Way. This estimate assumes the current population is complete out to 50 kpc, and increases to $91{{\ \rm per\ cent}}$ if the population is complete out to 150 kpc. The likelihood of there being two undiscovered clusters is between $60$ and $70{{\ \rm per\ cent}}$, with the likelihood of there being three undiscovered clusters being on the order of $50{{\ \rm per\ cent}}$. The most likely scenario is that the undiscovered clusters are moving outwards, which results in the outer cluster population being consistent with an equilibrium state. Searches for distant and possibly quite low concentration and very low metallicity globular clusters will be enabled with upcoming deep imaging surveys.

scholarly journals Dynamics of Globular Cluster Systems

1983 ◽  
Vol 100 ◽  
pp. 359-364
Author(s):  
K. C. Freeman
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Cluster Formation ◽  
Active Phase ◽  
Chemical Abundance ◽  
Cluster Systems ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Galaxy

In the Milky Way, the globular clusters are all very old, and we are accustomed to think of them as the oldest objects in the Galaxy. The clusters cover a wide range of chemical abundance, from near solar down to about [Fe/H] ⋍ −2.3. However there are field stars with abundances significantly lower than −2.3 (eg Bond, 1980); this implies that the clusters formed during the active phase of chemical enrichment, with cluster formation beginning at a time when the enrichment processes were already well under way.

scholarly journals LAMOST J011939.222−012150.45: The most barium-enhanced CEMP-s turnoff star

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Shilin Zhang ◽  
Haining Li ◽  
Gang Zhao ◽  
Wako Aoki ◽  
Tadafumi Matsuno
Keyword(s):  
Neutron Capture ◽  
Signal To Noise Ratio ◽  
Asymptotic Giant Branch ◽  
Velocity Variation ◽  
High Signal ◽  
Evolutionary Status ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Radial Velocity Variation ◽  
Carbon Excess

Abstract We have performed chemical abundance analyses for a newly discovered metal-poor turn-off star (Teff = 6276 K, log g = 3.93, [Fe$/$H] = −2.93), LAMOST J011939.222−012150.45, based on high-resolution and high signal-to-noise ratio spectra in both optical and near-UV obtained by Subaru. Abundances have been derived for 20 elements, including 11 light elements such as C, N, Na, Mg, etc., and 9 neutron-capture elements from Sr to Pb. This object is a carbon-enhanced metal-poor star with a large carbon excess of [C$/$Fe] = +2.26. LAMOST J011939.222−012150.45 shows extreme enhancement in s-process elements, especially for Ba, La, and Pb ([Ba$/$Fe] = +3.16 ± 0.18, [La$/$Fe] = +2.29 ± 0.24, [Pb$/$Fe] = +3.38 ± 0.12). A very clear radial velocity variation has also been detected, providing evidence of the existence of a companion. Interestingly, even without any scaling, the observed abundance pattern from light to heavy neutron-capture elements agrees well with predictions of accretion from a companion asymptotic giant branch (AGB) star. Considering the evolutionary status of this object, its surface material is very likely to be completely accreted from its AGB companion and has been preserved until today.

scholarly journals Similarities of the intermediate-age SMC star cluster NGC 152 with inner disk clusters in the Milky Way

1991 ◽  
Vol 148 ◽  
pp. 198-199
Author(s):  
T. Richtler ◽  
Klaas S. De Boer ◽  
A. Vallenari ◽  
W. Seggewiss
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Star Clusters ◽  
Star Cluster ◽  
Horizontal Branch ◽  
Vertical Extension ◽  
Magnitude Diagram ◽  
The Mean ◽  
Normal Feature ◽  
Selection Of

A colour-magnitude diagram (CMD) of the region containing the intermediate-age SMC globular cluster NGC 152 was published recently (Melcher & Richtler 1989). A particularly interesting feature of this CMD is the “clump” of He-core burning stars, which are predominantly field stars. A selection of stars near the cluster centre leads to the CMD shown in Figure 1. The vertical extension of the clump (explainable by the evolution of stars younger than 1 Gyr) is replaced by a “tilted horizontal branch” (we use this expression for lack of a better one). The age of NGC 152 is about 1.3 Gyr and the reddening is small; the metallicity is unknown but less than −0.6 dex, which is the mean metallicity of the young SMC population. The tilted HB can be reproduced in CMD simulations using the method developed by Vallenari et al. (1990), and thus can be considered as a normal feature of star clusters like NGC 152. It is evident also in other intermediate-age MC clusters like Kron 3 (Rich et al. 1984).

scholarly journals Spectroscopy of the Globular Clusters in M87

1987 ◽  
Vol 127 ◽  
pp. 451-452
Author(s):  
J.R. Mould ◽  
J.B. Oke ◽  
J.M. Nemec
Keyword(s):  
Density Distribution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Cluster System ◽  
Hot Gas ◽  
The Mean ◽  
Globular Cluster System ◽  
Young Clusters

With a velocity dispersion of 370 ± 50 km/sec the globular cluster system of M87 is kinematically hotter than the stars in the giant elliptical itself. This is consistent with the clusters' shallower density distribution for isotropic orbits. the mean metallicity of the 27 clusters in the sample analyzed here is no more than a factor of 2 more metal rich than the cluster system of the Milky Way, but considerably more metal poor than the integrated starlight in the field at a radius of 1' from the center of M87. There is no evidence for the existence of young clusters in the system. the mass-radius relation between 1' and 5' required to contain the globular clusters joins on to that required to contain the hot gas around M87.

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 Structure and Evolution of the Milky Way Galaxy

1989 ◽  
Vol 111 ◽  
pp. 83-102 ◽  
Author(s):  
Gerard Gilmore ◽  
Rosemary F.G. Wyse
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Axial Ratio ◽  
Thick Disk ◽  
The Sun ◽  
Chemical Abundance ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Available Information

AbstractThe combination of chemical abundance, kinematic, and age data for stars near the sun provides important information about the early evolution of the Galaxy. We review available data, with some new analysis, to show that the sum of all available information strongly suggests that the extreme population II subdwarf system formed during a period of rapid collapse of the proto-Galaxy. This subdwarf system now forms a flattened, pressure-supported distribution, with axial ratio ∼2:1. The thick disk formed subsequent to the subdwarf system. At least the metal-poor tail of the thick disk is comparable in age to the globular cluster system. The thick disk is probably kinematically discrete from the Galactic old disk, though the data remain inadequate for robust conclusions.

scholarly journals Enrichment of the Galactic disc with neutron-capture elements: Mo and Ru

2019 ◽  
Vol 489 (2) ◽  
pp. 1697-1708
Author(s):  
T Mishenina ◽  
M Pignatari ◽  
T Gorbaneva ◽  
C Travaglio ◽  
B Côté ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Signal To Noise Ratio ◽  
Cosmic Time ◽  
Average Error ◽  
Galactic Disc ◽  
Halo Stars ◽  
History Of ◽  
First Time ◽  
Better Than

ABSTRACT We present new observational data for the heavy elements molybdenum (Mo, Z = 42) and ruthenium (Ru, Z= 44) in F-, G-, and K-stars belonging to different substructures of the Milky Way. The range of metallicity covered is −1.0 < [Fe/H] <  + 0.3. The spectra of Galactic disc stars have a high resolution of 42 000 and 75 000 and signal-to-noise ratio better than 100. Mo and Ru abundances were derived by comparing the observed and synthetic spectra in the region of Mo i lines at 5506, 5533 Å for 209 stars and Ru i lines at 4080, 4584, 4757 Å for 162 stars using the LTE approach. For all the stars, the Mo and Ru abundance determinations are obtained for the first time with an average error of 0.14 dex. This is the first extended sample of stellar observations for Mo and Ru in the Milky Way disc, and together with earlier observations in halo stars it is pivotal in providing a complete picture of the evolution of Mo and Ru across cosmic time-scales. The Mo and Ru abundances were compared with those of the neutron-capture elements (Sr, Y, Zr, Ba, Sm, Eu). The complex nucleosynthesis history of Mo and Ru is compared with different Galactic Chemical Evolution (GCE) simulations. In general, present theoretical GCE simulations show underproduction of Mo and Ru at all metallicities compared to observations. This highlights a significant contribution of nucleosynthesis processes not yet considered in our simulations. A number of possible scenarios are discussed.

scholarly journals A high-precision abundance analysis of the nuclear benchmark star HD 20

2020 ◽  
Vol 635 ◽  
pp. A104 ◽  
Author(s):  
Michael Hanke ◽  
Camilla Juul Hansen ◽  
Hans-Günter Ludwig ◽  
Sergio Cristallo ◽  
Andrew McWilliam ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Galactic Halo ◽  
Nuclear Astrophysics ◽  
Light Element ◽  
Chemical Abundance ◽  
High Resolution Data ◽  
Intermediate Neutron ◽  
Gravity Measurements ◽  
Low Metallicity ◽  
Non Local

Metal-poor stars with detailed information available about their chemical inventory pose powerful empirical benchmarks for nuclear astrophysics. Here we present our spectroscopic chemical abundance investigation of the metal-poor ([Fe/H] = −1.60 ± 0.03 dex), r-process-enriched ([Eu/Fe] = 0.73 ± 0.10 dex) halo star HD 20, using novel and archival high-resolution data at outstanding signal-to-noise ratios (up to ∼1000 Å−1). By combining one of the first asteroseismic gravity measurements in the metal-poor regime from a TESS light curve with the spectroscopic analysis of iron lines under non-local thermodynamic equilibrium conditions, we derived a set of highly accurate and precise stellar parameters. These allowed us to delineate a reliable chemical pattern that is comprised of solid detections of 48 elements, including 28 neutron-capture elements. Hence, we establish HD 20 among the few benchmark stars that have nearly complete patterns and low systematic dependencies on the stellar parameters. Our light-element (Z ≤ 30) abundances are representative of other, similarly metal-poor stars in the Galactic halo that exhibit contributions from core-collapse supernovae of type II. In the realm of the neutron-capture elements, our comparison to the scaled solar r-pattern shows that the lighter neutron-capture elements (Z ≲ 60) are poorly matched. In particular, we find imprints of the weak r-process acting at low metallicities. Nonetheless, by comparing our detailed abundances to the observed metal-poor star BD +17 3248, we find a persistent residual pattern involving mainly the elements Sr, Y, Zr, Ba, and La. These are indicative of enrichment contributions from the s-process and we show that mixing with material from predicted yields of massive, rotating AGB stars at low metallicity improves the fit considerably. Based on a solar ratio of heavy- to light-s elements – which is at odds with model predictions for the i-process – and a missing clear residual pattern with respect to other stars with claimed contributions from this process, we refute (strong) contributions from such astrophysical sites providing intermediate neutron densities. Finally, nuclear cosmochronology is used to tie our detection of the radioactive element Th to an age estimate for HD 20 of 11.0 ± 3.8 Gyr.

scholarly journals Gaia DR2 orbital properties for field stars with globular cluster-like CN band strengths

2019 ◽  
Vol 624 ◽  
pp. L9 ◽  
Author(s):  
A. Savino ◽  
L. Posti
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Light Element ◽  
Small Population ◽  
Sloan Digital Sky Survey ◽  
Element Abundances ◽  
Halo Stars ◽  
Sky Survey ◽  
Gaia Dr2

Context. Large spectroscopic surveys of the Milky Way have revealed that a small population of stars in the halo have light element abundances comparable to those found in globular clusters. The favoured explanation for the peculiar abundances of these stars is that they originated inside a globular cluster and were subsequently lost. Aims. Using orbit calculations we assess the likelihood that an existing sample of 57 field stars with globular cluster-like CN band strength originated in any of the currently known Milky Way globular clusters. Methods. Using Sloan Digital Sky Survey and Gaia data, we determine orbits and integrals of motion of our sample of field stars, and use these values and metallicity to identify likely matches to globular clusters. The pivot hypothesis is that had these stars been stripped from such objects, they would have remained on very similar orbits. Results. We find that ∼70% of the sample of field stars have orbital properties consistent with the halo of the Milky Way; however, only 20 stars have likely orbital associations with an existing globular cluster. The remaining ∼30% of the sample have orbits that place them in the outer Galactic disc. No cluster of similar metallicity is known on analogous disc orbits. Conclusions. The orbital properties of the halo stars seem to be compatible with the globular cluster escapee scenario. The stars in the outer disc are particularly surprising and deserve further investigation to establish their nature.

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