Evolutionary Aspects of the CMD of NGC 6553

We have investigated the V, B – V “clump” morphology of the globular cluster NGC 6553 (Ortolani et al. 1990, OBB90) through synthetic horizontal branch (SHB) models. Catelan's (1993) computations were extended to more metal-rich compositions, following Sweigart (1987) and Castellani et al. (1991), and transposed to the observational plane on the basis of VandenBerg's (1992) colour transformations and bolometric corrections. Observational scatter has also been added. In general, the SHB models are very clumpy, unlike the observed feature, which seems extended and peculiarly tilted. However, for particular combinations of helium abundance, metallicity, and mean mass on the HB, tilted models result, being however significantly less sloped and wider than observed. The NGC 6553 field is differentially reddened by ΔE(B – V) ≈ 0.06 (OBB90), which has been modelled, but which implies a CMD scatter which is smaller than the one originating from evolution away from the zero-age HB alone. We have also investigated the age of the cluster (ΔV method) and location of the red giant branch “bump,” in comparison with 47 Tuc. Since the helium and α-elements abundances are not known for NGC 6553, three chemical evolution scenarios have been considered, following the method of de Freitas Pacheco (1993). Details can be found elsewhere (Catelan et al. 1994).

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The Influence of Rotation on Horizontal Branch Stars and on RR Lyrae Pulsational Properties

Symposium - International Astronomical Union ◽

10.1017/s0074180900074039 ◽

1981 ◽

Vol 93 ◽

pp. 275-275

Author(s):

V. Castellani

Keyword(s):

Globular Cluster ◽

Main Sequence ◽

Horizontal Branch ◽

Structural Variations ◽

Rr Lyrae ◽

Horizontal Branch Stars ◽

Mass Size ◽

Red Giant

The occurrence of rotation in Globular Cluster stars has been suggested (see e.g. Renzini 1977) as a mechanism producing the observed colour spread in actual Horizontal Branches. If this is the case, canonical results on evolutionary properties of HB stars have to be revisited in order to account for rotation-driven structural variations: faster Main Sequence rotators delay the He flash increasing the mass-size Mc of the He core at the flash and loosing a greater amount of mass during the Red Giant stage.

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The Globular Cluster NGC 6144 and its Neighbouring Region

Symposium - International Astronomical Union ◽

10.1017/s007418090009224x ◽

1980 ◽

Vol 85 ◽

pp. 421-421

Author(s):

G. Alcaino

Keyword(s):

Galactic Plane ◽

Galactic Centre ◽

Horizontal Branch ◽

Giant Star ◽

Horizontal Branch Stars ◽

Metal Deficiency ◽

Magnitude Diagram ◽

Neighbouring Region ◽

Red Giant ◽

The One

NGC 6144 is situated in the general area behind the nebulosity in Scorpio-Ophiuchus between its counterpart M4 and the bright red giant star Antares. The color magnitude diagram (CMD) is characterized by a steep giant branch, a group of exclusively blue horizontal branch stars, and a well defined instability gap within the colour range ~0.4 < B-V < 0.8. The CMD has the typical features of metal poor clusters, similar to M3, M15, and M92. From the analysis of five circular areas equal to the one measured in the cluster, it is shown that absorption increases towards the NE direction. The deduced reddening of E(B-V)=0.40 places the object at 15.8 kpc from the Sun, 4.3 kpc from the galactic plane and 7.8 kpc from the galactic centre, assuming Ro=9 kpc. The inferred values of δV~3.1 and S~5, corroborate the tendency of metal deficiency suggested by the integrated colours, which render Q=-0.41.

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Images in the rocket ultraviolet - The initial helium abundance and distance modulus of the globular cluster M5 from photometry of horizontal-branch stars

The Astrophysical Journal ◽

10.1086/163200 ◽

1985 ◽

Vol 292 ◽

pp. 687 ◽

Cited By ~ 7

Author(s):

R. C. Bohlin ◽

R. H. Cornett ◽

J. K. Hill ◽

A. M. Smith ◽

T. P. Stecher

Keyword(s):

Globular Cluster ◽

Distance Modulus ◽

Helium Abundance ◽

Horizontal Branch ◽

Horizontal Branch Stars

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THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS

The Astronomical Journal ◽

10.1088/0004-6256/141/6/175 ◽

2011 ◽

Vol 141 (6) ◽

pp. 175 ◽

Cited By ~ 187

Author(s):

Jennifer S. Sobeck ◽

Robert P. Kraft ◽

Christopher Sneden ◽

George W. Preston ◽

John J. Cowan ◽

...

Keyword(s):

Globular Cluster ◽

Neutron Capture ◽

Horizontal Branch ◽

Horizontal Branch Stars ◽

Red Giant

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The GOTHAM survey: chemical evolution of Milky Way globular clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317007086 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 25-28

Author(s):

Bruno Dias ◽

Beatriz Barbuy ◽

Ivo Saviane ◽

Enrico V. Held ◽

Gary Da Costa ◽

...

Keyword(s):

Chemical Evolution ◽

Globular Cluster ◽

Globular Clusters ◽

Stellar Population ◽

Milky Way ◽

Open Clusters ◽

Giant Stars ◽

Globular Cluster System ◽

Galactic Globular Clusters ◽

Red Giant

AbstractMilky Way globular clusters are excellent laboratories for stellar population detailed analysis that can be applied to extragalactic environments with the advent of the 40m-class telescopes like the ELT. The globular cluster population traces the early evolution of the Milky Way which is the field of Galactic archaeology. We present our GlObular clusTer Homogeneous Abundance Measurement (GOTHAM) survey. We derived radial velocities, Teff, log(g), [Fe/H], [Mg/Fe] for red giant stars in one third of all Galactic globular clusters that represent well the Milky Way globular cluster system in terms of metallicity, mass, reddening, and distance. Our method is based on low-resolution spectroscopy and is intrinsically reddening free and efficient even for faint stars. Our [Fe/H] determinations agree with high-resolution results to within 0.08 dex. The GOTHAM survey provides a new metallicity scale for Galactic globular clusters with a significant update of metallicities higher than [Fe/H] > -0.7. We show that the trend of [Mg/Fe] with metallicity is not constant as previously found, because now we have more metal-rich clusters. Moreover, peculiar clusters whose [Mg/Fe] does not match Galactic stars for a given metallicity are discussed. We also measured the CaII triplet index for all stars and we show that the different chemical evolution of Milky Way open clusters, field stars, and globular clusters implies different calibrations of calcium triplet to metallicity.

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Horizontal Branch Evolution and RR Lyrae Star Pulsation

Highlights of Astronomy ◽

10.1017/s1539299600012193 ◽

1995 ◽

Vol 10 ◽

pp. 590-593 ◽

Cited By ~ 1

Author(s):

Arthur N. Cox

Keyword(s):

Stellar Evolution ◽

Globular Clusters ◽

Deep Convection ◽

Big Bang ◽

Helium Abundance ◽

Horizontal Branch ◽

Rr Lyrae ◽

Red Giant ◽

The Masses ◽

The Big Bang

For many years there has been a confrontation between stellar evolution and pulsation theories concerning the masses, luminosities, and compositions of the horizontal branch RR Lyrae variables. Masses obtained by Cox, Hodson & Clancy (CHC, 1983) were very low, but Kovacs (1985) and later Kovacs & Buchler (1988) suggested somewhat larger ones. Even later Simon & Cox (1991) verified CHC results, though still using the Los Alamos opacities. Petersen (1991, 1992) has also discussed this mass problem in some detail. The persistent discrepancy of 0.1 Mʘ or more between the evolution and pulsation masses was mostly ignored because neither theory could find any significant flaw in its analysis. Cox (1991), Kovacs, Buchler & Marom (1991), and Kovacs, Buchler, Marom, Iglesias & Rogers (1992) finally showed that larger double-mode pulsation masses, are consistent with evolution calculations to reproduce color-magnitude diagrams of globular clusters. Evolution tracks by many for years, especially the recent ones by Lee, Demarque & Zinn (1990), did require a much lower primordial helium abundance near the big bang value near Y = 0.23, and now this value, slightly enhanced by deep convection dredge-up in the earlier red giant stage, is also found to be appropriate for pulsation studies.

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On the Number Ratio of Horizontal Branch Stars to Red Giant Stars in Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900074088 ◽

1981 ◽

Vol 93 ◽

pp. 284-284

Author(s):

N. Arimoto ◽

M. Simoda

Keyword(s):

Globular Clusters ◽

Big Bang ◽

Helium Abundance ◽

Horizontal Branch ◽

Giant Stars ◽

Horizontal Branch Stars ◽

Significant Difference ◽

Red Giant Stars ◽

The Difference ◽

Red Giant

The number ratios of horizontal branch stars to red giant stars were obtained for globular clusters and Draco dwarf galaxy and the helium abundance was estimated using model results without semiconvection zone (SCZ) and with fully developed one. The analysis was confined to the four clusters (M4, M5, M13, and 47 Tuc) and the Draco galaxy, for which fairly precise star counts had been carried out. The effect of the difference in radial distribution between horizontal and red giant branch stars were taken into account, if necessary. The statistically significant difference in R exists among these objects. The cause may be the difference in the helium abundance and/or in the development of the SCZ. In the case of the fully developed SCZ, the helium abundance for M5 and Draco is appreciably smaller than the value given by the big-bang cosmology. It may be taken as an evidence against the full development of the SCZ for the horizontal branch stars in these objects.

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Are Galactic globular cluster AGB stars rich or poor in Sodium? Sodium abundance of AGB and RGB stars in NGC 2808

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008681 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 361-362

Author(s):

Yue Wang ◽

Francesca Primas ◽

Corinne Charbonnel ◽

Mathieu Van der Swaelmen ◽

William Chantereau ◽

...

Keyword(s):

Spectroscopic Study ◽

Globular Cluster ◽

Main Sequence ◽

Significant Fraction ◽

Agb Stars ◽

2Nd Generation ◽

Red Giant ◽

Sodium Abundance

AbstractA spectroscopic study comparing the [Na/Fe] distributions of RGB and AGB stars in the Galactic globular cluster (GC) NGC 6752 found that there was no Na-rich, 2nd-generation star along the early-AGB of this cluster. This came as a surprise since in this GC, as well as other Galactic GCs studied so far, 1st- and 2nd-generation stars have usually been found from the main sequence turnoff up to the red giant branch. To investigate whether the failure of a significant fraction of stars to ascend the AGB also happens to other GCs, we studied a sample of AGB and RGB stars in NGC 2808 observed at the ESO/VLT with FLAMES. Contrary to NGC 6752, we find that the AGB and RGB stars we studied in NGC 2808 have comparable [Na/Fe] dispersions.

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