scholarly journals Photometry of the Globular Cluster NGC 5466: Red Giants and Blue Stragglers

2007 ◽  
Vol 663 (1) ◽  
pp. 277-295 ◽  
Author(s):  
Nassissie Fekadu ◽  
Eric L. Sandquist ◽  
Michael Bolte
Keyword(s):  
Globular Cluster ◽  
Red Giants ◽  
Blue Stragglers

Blue stragglers in the core of the globular cluster 47 Tucanae

Nature ◽  
1991 ◽  
Vol 352 (6333) ◽  
pp. 297-301 ◽  
Author(s):  
F. Paresce ◽  
M. Shara ◽  
G. Meylan ◽  
D. Baxter ◽  
P. Greenfield ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Blue Stragglers ◽  
The Core

scholarly journals Hubble Space TelescopeObservations of NGC 121: First Detection of Blue Stragglers in an Extragalactic Globular Cluster

1998 ◽  
Vol 508 (2) ◽  
pp. 570-575 ◽  
Author(s):  
Michael M. Shara ◽  
S. Michael Fall ◽  
R. Michael Rich ◽  
David Zurek
Keyword(s):  
Globular Cluster ◽  
Blue Stragglers

scholarly journals Evidence for Mass Segregation in NGC 5466

1988 ◽  
Vol 126 ◽  
pp. 677-678
Author(s):  
James M. Nemec ◽  
Hugh C. Harris
Keyword(s):  
Globular Cluster ◽  
Binary Systems ◽  
Low Frequency ◽  
Close Binary ◽  
Photoelectric Photometry ◽  
Significance Level ◽  
Blue Stragglers ◽  
Mass Segregation ◽  
The Masses ◽  
Subgiant Stars

Forty-eight blue straggler stars have been discovered in NGC 5466, the only Galactic globular cluster known to contain an anomalous Cepheid of the sort found in dwarf galaxies. The stars were identified in color-magnitude diagrams constructed from photometry of deep photographic plates taken with the Canada-France-Hawaii 3.6 m telescope (calibrated with new UBV photoelectric photometry), and from point spread function photometry of CCD frames taken with the Palomar 5 m telescope. The stars typically have magnitudes <V> ~ 19.m1 and colors <B-V> ~ 0.m2. Forty-two of the 48 stars are situated inside of R=2.5 arcmin (see Fig.1), the projected radius containing half the cluster luminosity, and only six stars are found between 2.5 and 9 arcmin. A one-sided, two-sample Kolmogorov-Smirnov test (using the CCD data) establishes at the 98% significance level that the blue stragglers are more centrally concentrated than the subgiant stars of the same magnitude. By fitting multi-component King models to the projected radial distributions (Fig.2), the mean mass of the blue stragglers is shown to be ~1.5 to two times larger than the masses of the stars that contributed the light from which the core and tidal radii were derived (i.e. M (Blue Str.)=1.3±0.3 M⊙). Because the central relaxation time for NGC 5466 is much less than the cluster age, the different radial distributions are attributed to mass segregation. A similar mass segregation is also observed in the globular cluster NGC 5053, where Nemec and Cohen (1986, in preparation) have recently identified ~30 blue stragglers. The low stellar density and small escape velocity of NGC 5466 make a recent epoch of star formation (during which the blue stragglers might have formed as massive single stars) seem unlikely. Instead, the blue stragglers probably are either close binary systems that have transferred mass, or are coalesced stars. The very low frequency of stellar collisions expected in the center of NGC 5466 suggests that the blue stragglers are primordial binary systems. The simultaneous presence in NGC 5466 of the blue stragglers and the anomalous Cepheid V19, and their relative numbers, supports the hypothesis that there is an evolutionary connection between the two types of stars. By fitting theoretical isochrones to the photographic c-m diagram, NGC 5466 is estimated to have an age of 18±3 Gyr.

scholarly journals The Hertzsprung-Russell Diagram of Metal-Poor Disk Stars

1978 ◽  
Vol 80 ◽  
pp. 273-276
Author(s):  
Sidney van den Bergh
Keyword(s):  
Velocity Field ◽  
Globular Cluster ◽  
High Velocity ◽  
Population Model ◽  
Open Cluster ◽  
Ultraviolet Excess ◽  
Red Giants ◽  
The Sun ◽  
The Galaxy ◽  
Red Giant

A quarter of a century ago Keenan and Keller (1953) showed that the majority of high-velocity stars near the Sun outline a Hertzsprung-Russell diagram similar to that of old Population I. This result, which did not appear to fit into Baade's (1944) two-population model of the Galaxy was ignored (except by Roman 1965) for the next two decades. Striking confirmation of the results of Keenan and Keller was, however, obtained by Hartwick and Hesser (1972). Their work appears to show that high-velocity field stars with an ultraviolet excess (which measures Fe/H) of δ(U-B) ≃ +0m.11 lie on a red giant branch that is more than a magnitude fainter than the giant branch of the strong-lined globular cluster 47 Tuc for which δ(U-B) ≃ +0m.10. Furthermore Demarque and McClure (1977) show that the red giants in the old metal poor [δ(U-B) ≃ +0m.11] open cluster NGC 2420 are significantly fainter than are those in 47 Tuc. Calculations by these authors show that the observed differences between the giants in 47 Tuc and in NGC 2420 can be explained if either (1) 47 Tuc is richer in helium than NGC 2420 by ΔY ≃ 0.1 or (2) if 47 Tuc has a ten times lower value of Z(CNO) than does NGC 2420.

Stellar encounters involving red giants in globular cluster cores

1991 ◽  
Vol 381 ◽  
pp. 449 ◽  
Author(s):  
M. B. Davies ◽  
W. Benz ◽  
J. G. Hills
Keyword(s):  
Globular Cluster ◽  
Red Giants ◽  
Cluster Cores

scholarly journals The Globular Cluster Terzan 7 in the Sagittarius Dwarf Spheroidal Galaxy

2002 ◽  
Vol 207 ◽  
pp. 165-167
Author(s):  
Enrico V. Held ◽  
Alfred Rosenberg ◽  
Ivo Saviane ◽  
Yazan Momany
Keyword(s):  
Globular Cluster ◽  
Cluster System ◽  
New Method ◽  
Blue Stragglers ◽  
Globular Cluster System

We present deep V, I photometry of the globular cluster Terzan 7, a probable member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. The metallicity, estimated from a new method based on analytic RGB fits, agrees with previous estimates based on color-magnitude diagrams ([Fe/H]= −0.9 ± 0.1 dex). This result confirms a discrepancy between photometric and spectroscopic determinations. Using both the horizontal and vertical methods to estimate relative ages, we confirm that the age of Terzan 7 is about 70% that of 47 Tuc. A rich population of blue stragglers is found, strongly concentrated toward the center of the cluster.

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