scholarly journals On a Physical Mechanism for Extra-Mixing in Globular Cluster Red Giants

2002 ◽  
Vol 12 ◽  
pp. 289-291
Author(s):  
Pavel A. Denissenkov ◽  
Christopher A. Tout
Keyword(s):  
Globular Cluster ◽  
Turbulent Diffusion ◽  
Globular Clusters ◽  
Physical Mechanism ◽  
Meridional Circulation ◽  
Red Giants ◽  
Joint Operation ◽  
Radiative Zone ◽  
Rotating Star ◽  
First Time

AbstractFor the first time we propose a real physical mechanism for extra-mixing in red giants which canquantitativelyinterpret all the known star-to-star abundance variations in globular clusters. This is Zahn’s mechanism (Zahn 1992; Maeder & Zahn 1998). It considers extra-mixing in a radiative zone of a rotating star as a result of joint operation of meridional circulation and turbulent diffusion.

scholarly journals A nitrogen-enhanced metal-poor star discovered in the globular cluster ESO280−SC06

2019 ◽  
Vol 490 (1) ◽  
pp. 741-751 ◽  
Author(s):  
Jeffrey D Simpson ◽  
Sarah L Martell
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Binary Systems ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Horizontal Branch ◽  
Term Survival ◽  
Abundance Patterns ◽  
Metal Poor Star

ABSTRACT We report the discovery of the only very nitrogen-enhanced metal-poor star known in a Galactic globular cluster. This star, in the very metal-poor cluster ESO280−SC06 , has $[\textrm{N}/\textrm{Fe}]\, \gt +2.5$, while the other stars in the cluster show no obvious enhancement in nitrogen. Around 80 NEMP stars are known in the field, and their abundance patterns are believed to reflect mass transfer from a binary companion in the asymptotic giant branch phase. The dense environment of globular clusters is detrimental to the long term survival of binary systems, resulting in a low observed binary fraction among red giants and the near absence of NEMP stars. We also identify the first known horizontal branch members of ESO280−SC06 , which allow for a much better constraint on its distance. We calculate an updated orbit for the cluster based on our revised distance of 20.6 ± 0.5 kpc, and find no significant change to its orbital properties.

scholarly journals Red Giants in Globular Clusters and Large-Scale Variations in The Galaxy

1980 ◽  
Vol 5 ◽  
pp. 817-826
Author(s):  
B. E. J. Pagel
Keyword(s):  
Recent Work ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Large Scale ◽  
Red Giants ◽  
Mixing Effects ◽  
The Galaxy ◽  
Metal Abundance ◽  
Red Giant

SummaryThis review concerns recent work on the determination of overall metallicities [Fe/H] in a number of globular clusters and the systematics of mixing effects displayed (usually) by weak CH and strong CN. Special attention is given to the globular cluster ω Centauri, where both metal abundance variations and mixing effects occur and are closely intertwined. Recent observations carried out at the Anglo-Australian Telescope by E.A. Mallia and D.C. Watts have revealed large variations in the strength of metallic lines across the red giant branch of this cluster.

scholarly journals On the absence of symbiotic stars in globular clusters

2020 ◽  
Vol 496 (3) ◽  
pp. 3436-3447
Author(s):  
Diogo Belloni ◽  
Joanna Mikołajewska ◽  
Krystian Iłkiewicz ◽  
Matthias R Schreiber ◽  
Mirek Giersz ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Relaxation Times ◽  
Low Density ◽  
Symbiotic Stars ◽  
Population Synthesis ◽  
Galactic Field ◽  
Nearby Galaxies ◽  
Orbital Periods ◽  
First Time

ABSTRACT Even though plenty of symbiotic stars (SySts) have been found in the Galactic field and nearby galaxies, not a single one has ever been confirmed in a Galactic globular cluster (GC). We investigate the lack of such systems in GCs for the first time by analysing 144 GC models evolved with the mocca code, which have different initial properties and are roughly representative of the Galactic GC population. We focus here on SySts formed through the wind-accretion channel, which can be consistently modelled in binary population synthesis codes. We found that the orbital periods of the majority of such SySts are sufficiently long (≳103 d) so that, for very dense GC models, dynamical interactions play an important role in destroying their progenitors before the present day (∼11–12 Gyr). In less dense GC models, some SySts are still predicted to exist. However, these systems tend to be located far from the central parts (≳70 per cent are far beyond the half-light radius) and are sufficiently rare (≲1 per GC per Myr), which makes their identification rather difficult in observational campaigns. We propose that future searches for SySts in GCs should be performed in the outskirts of nearby low-density GCs with sufficiently long half-mass relaxation times and relatively large Galactocentric distances. Finally, we obtained spectra of the candidate proposed in ω Cen (SOPS IV e-94) and showed that this object is most likely not a SySt.

UBV Photometry of RR Lyrae Variables in the Globular Cluster M4

1979 ◽  
Vol 46 ◽  
pp. 347-354 ◽  
Author(s):  
Carla Cacciari
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Normal Metal ◽  
Red Giants ◽  
The Sun ◽  
Horizontal Branch ◽  
Dark Clouds ◽  
Rr Lyrae ◽  
Metal Abundance ◽  
Ubv Photometry

M4, one of the closest globular clusters to the Sun, presents some peculiar features that make it very interesting to study. The first C-M diagram, published by Greenstein (1939), showed a well populated blue-horizontal branch, a characteristic which usually, but not always, indicates low metal abundance (Hartwick 1968). Kinman (1959) found however that it contains strong lined red giants and classified it as type A, indicating normal metal abundance. More recent C-M diagrams (Moshkalev 1975, Alcaino 1975, Lee 1977, Lloyd Evans 1977) substantially confirmed both these characteristics.One of the major problems in the study of this cluster is the high and possibly non-uni form reddening, due to its location behind the Scorpius-Ophiuchus dark clouds.

scholarly journals M31 Globular Clusters in the Near-Infrared

2002 ◽  
Vol 207 ◽  
pp. 152-153
Author(s):  
Wolfgang Brandner ◽  
R. Brent Tully ◽  
James N. Heasley
Keyword(s):  
Old Age ◽  
Adaptive Optics ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Near Infrared ◽  
Time Resolved ◽  
Red Giant ◽  
The University ◽  
First Time ◽  
Adaptive Optics System

We have observed the M31 globular clusters with the University of Hawaii Adaptive Optics System Hokupa'a at the Gemini North 8m telescope on Mauna Kea. This is part of a project which aims at spatially resolving intermediate-age and old-age stellar populations in the Local Volume and beyond - possibly out to distances of the Virgo and Fornax clusters. The sparse M31 globular cluster G27 (Hubble 6) is for the first time resolved into individual stars. The tip of the red giant branch (TRGB) at K≈18.8mag yields a metallicity of Z around 0.001 solar for G27.

scholarly journals Abundance of zirconium in the atmospheres of red giants in Galactic globular cluster 47 Tuc

2019 ◽  
Vol 14 (S351) ◽  
pp. 309-311
Author(s):  
Edgaras Kolomiecas ◽  
Vidas Dobrovolskas ◽  
Arūnas Kučinskas
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Stellar Model ◽  
Red Giants ◽  
Line Profiles ◽  
Galactic Field ◽  
Galactic Globular Clusters ◽  
Red Giant

AbstractWe determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostaticATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with theSYNTHE package. The average zirconium abundance determined in the sample of RGB stars, 〈[Zr/Fe]〉 = +0.38 ± 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.

scholarly journals High-resolution abundance analysis of four red giants in the globular cluster NGC 6558

2018 ◽  
Vol 619 ◽  
pp. A178 ◽  
Author(s):  
B. Barbuy ◽  
L. Muniz ◽  
S. Ortolani ◽  
H. Ernandes ◽  
B. Dias ◽  
...  
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Abundance Ratio ◽  
Mean Value ◽  
Heavy Elements ◽  
Spectroscopic Parameter ◽  
Red Giants ◽  
Abundance Pattern ◽  
Element Abundances

Context. NGC 6558 is a bulge globular cluster with a blue horizontal branch (BHB), combined with a metallicity of [Fe/H] ≈ −1.0. It is similar to HP 1 and NGC 6522, which could be among the oldest objects in the Galaxy. Element abundances in these clusters could reveal the nature of the first supernovae. Aims. We aim to carry out detailed spectroscopic analysis for four red giants of NGC 6558, in order to derive the abundances of the light elements C, N, O, Na, Al, the α-elements Mg, Si, Ca, Ti, and the heavy elements Y, Ba, and Eu. Methods. High-resolution spectra of four stars with FLAMES-UVES at VLT UT2-Kueyen were analysed. Spectroscopic parameter-derivation was based on excitation and ionization equilibrium of Fe I and Fe II. Results. This analysis results in a metallicity of [Fe/H] = − 1.17 ± 0.10 for NGC 6558. We find the expected α-element enhancements in O and Mg with [O/Fe] = +0.40, [Mg/Fe] = +0.33, and low enhancements in Si and Ca. Ti has a moderate enhancement of [Ti/Fe] = +0.22. The r-element Eu appears very enhanced with a mean value of [Eu/Fe] = +0.63. The first peak s-elements Y and Sr are also enhanced, these results have however to be treated with caution, given the uncertainties in the continuum definition; the use of neutral species (Sr I, Y I), instead of the dominant ionized species is another source of uncertainty. Ba appears to have a solar abundance ratio relative to Fe. Conclusions. NGC 6558 shows an abundance pattern that could be typical of the oldest inner bulge globular clusters, together with the pattern in the similar clusters NGC 6522 and HP 1. They show low abundances of the odd-Z elements Na and Al, and of the explosive nucleosynthesis α-elements Si, Ca, and Ti. The hydrostatic burning α-elements O and Mg are normally enhanced as expected in old stars enriched with yields from core-collapse supernovae, and the iron-peak elements Mn, Cu, Zn show low abundances, which is expected for Mn and Cu, but not for Zn. Finally, the cluster trio NGC 6558, NGC 6522, and HP 1 have relatively high abundances of first-peak heavy elements, variable second-peak element Ba, and the r-element Eu is enhanced. The latter is particularly high in NGC 6558.

Recent Advances in High Dispersion Spectroscopy of Globular Cluster Stars

1988 ◽  
Vol 132 ◽  
pp. 525-530
Author(s):  
Raffaele G. Gratton
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
High Dispersion ◽  
Photographic Material ◽  
Recent Advances ◽  
Metal Abundances ◽  
Ccd Detectors ◽  
Major Progress

The use CCD detectors has allowed a major progress in abundance derivations for globular cluster stars in the last years. Abundances deduced from high dispersion spectra now correlates well with other abundance indicators. I discuss some problems concerning the derivation of accurate metal abundances for globular clusters using high dispersion spectra from both the old photographic and the most recent CCD data. The discrepant low abundances found by Cohen (1980), from photographic material for M71 giants, are found to be due to the use of too high microturbulences.

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