The helium content of the peculiar Oosterhoff type I globular cluster ? Centauri

1981 ◽  
Vol 76 (2) ◽  
pp. 329-339 ◽  
Author(s):  
Filippina Caputo
Keyword(s):  
Globular Cluster ◽  
Type I ◽  
Helium Content

scholarly journals The Oosterhoff Period Effect and the Age of the Galactic Globular Cluster System

1993 ◽  
Vol 139 ◽  
pp. 3-14
Author(s):  
Allan Sandage
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Hubble Constant ◽  
Cluster System ◽  
Period Effect ◽  
Type I ◽  
Instability Strip ◽  
Cluster Data ◽  
Globular Cluster System ◽  
The Individual

AbstractThe Oosterhoff division of globular clusters into two dichotomous mean period groups is a result of the variation with metallicity of the combined effects of (1) a mean increase in period with decreasing metallicity, and (2) the change of globular cluster horizontal branch (HB) morphology from the M3 to the M13 HB type within the instability strip in the metallicity range of [Fe/H] between -1.7 and -1.9. A new representation of the Oosterhoff period effect showing this property is made from the individual cluster data in Figure 1. The relation between period and metallicity for cluster and for field RR Lyraes at the blue fundamental edge of the instability strip in the HR diagram as read from this figure islog Pab = -0.122(±0.02)([Fe/H]) - 0.500(±0.01)using the metallicity scale of Butler.The high slope coefficient is consistent with the extant models of the HB when they are read at the varing temperature of the fundamental blue edge given by equation (3) of the text. Most of the current literature treats only the constant temperature condition, which is manifestly incorrect. It is this temperature effect that reconciles the observations and the models.A new calibration of the absolute magnitudes of RR Lyrae stars as a function of metallicity, combined with new oxygen enhanced isochrones for globular clusters (Bergbusch & VandenBerg 1992) reduces the age of the Galactic globular cluster system to 14.1 ± 0.3 Gyr (internal error). The resulting lower age of the universe which, when combined with a Hubble constant near 50 km s-1 Mpc-1 determined from type I supernovae, shows that the cosmological expansion has been decelerated by an amount consistent with the closure density, permitting Ω ∼ 1 now from the timing test.

scholarly journals Globular Cluster Luminosity Functions

1988 ◽  
Vol 126 ◽  
pp. 121-131
Author(s):  
Pierre Demarque
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Structure ◽  
Structure Theory ◽  
Initial Mass ◽  
Helium Content ◽  
Luminosity Functions

The use of luminosity functions in the following areas is reviewed: (a) the determination of the helium content and ages of the globular clusters; (b) the testing of stellar structure theory; and (c) the determination of the initial mass function of globular clusters.

scholarly journals Do Halo Field Stars and Globular Clusters Belong to the Same Population?

1983 ◽  
Vol 6 ◽  
pp. 129-137 ◽  
Author(s):  
Robert P. Kraft
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Helium Content ◽  
The Past ◽  
Solar Motion ◽  
Trigonometric Parallaxes ◽  
The Common ◽  
Existent Problem

Obviously such transcendental issues as the helium content and age of the oldest stars depend on whether we are correct in our belief that the answer to this question is “yes” I hardly need say that over the past 40 years compelling affirmative arguments have been developed. Thus, for example, the solar motion of the common subdwarfs can be shown (e.g., Carney 1979) to be essentially identical with that of globular clusters (Kinman 1959) (Table 1), and the Fe-peak metallicities of giants and RR Lyraes in the halo field have been shown to be the same as those in clusters [see, e.g., recent reviews by Kraft (1979) and Freeman and Norris (1981)]. It is hard to believe that we would be incorrect in identifying the main sequence of a globular cluster with the main sequence defined by the trigonometric parallaxes, magnitudes and colors of subdwarfs having the same [Fe/H]. It might seem, therefore, that raising such an issue at this late date is equivalent to discussing a non-existent problem.

scholarly journals Blazhko-type fundamental-mode RR Lyrae stars in the globular cluster M3

2019 ◽  
Vol 490 (1) ◽  
pp. 80-95 ◽  
Author(s):  
J Jurcsik
Keyword(s):  
Globular Cluster ◽  
Fundamental Mode ◽  
Stellar System ◽  
Relative Strength ◽  
Similar Distribution ◽  
Type I ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Mean ◽  
Lyrae Stars

ABSTRACT Blazhko stars from the extended BVIC time series of RRab stars in the globular cluster M3 are analysed. This is the largest sample of Blazhko stars with full details of their Blazhko properties in a homogeneous stellar system. Blazhko periods and light-curve solutions are determined/estimated for 83 fundamental-mode variables. The lack of phase modulation in Oosterhoff type II stars and the diminishing relative strength of the modulation in long-period Oosterhoff type I stars are regular tendencies found between the pulsation and modulation properties of Blazko stars. Similarly to previous results, no modulation of the longest-period stars is detected. The onset of modulation in a previously regular RRab star and the similar distribution of modulated and non-modulated stars imply that the modulation is a temporal property of RR Lyrae (RRL) stars, which may occur at any time in any RRab star except the coolest ones. Comparing the modulation periods in M3 and in other samples of Blazhko stars, the mean log(Pmod) value is found to depend on the metallicity of the system. The separation of temperature- and radius-change induced variations supports our previous finding that the photometric radius variation does not show any modulation. The pulsation-averaged mean brightness and temperature of Blazhko stars are found to be larger in the large-amplitude phase of the modulation than in the small-amplitude phase. The larger the amplitude of the modulation, the larger the changes of the mean parameters detected.

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.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

Heat-Etching with a Bullivant Type II Simple Freeze-Cleave Device

1970 ◽  
Vol 28 ◽  
pp. 106-107 ◽  
Author(s):  
Ronald S. Weinstein ◽  
N. Scott McNutt
Keyword(s):  
New Zealand ◽  
General Hospital ◽  
Massachusetts General Hospital ◽  
Type I ◽  
Type Ii ◽  
Collaborative Effort ◽  
Temperature And Pressure ◽  
The University

The Type I simple cold block device was described by Bullivant and Ames in 1966 and represented the product of the first successful effort to simplify the equipment required to do sophisticated freeze-cleave techniques. Bullivant, Weinstein and Someda described the Type II device which is a modification of the Type I device and was developed as a collaborative effort at the Massachusetts General Hospital and the University of Auckland, New Zealand. The modifications reduced specimen contamination and provided controlled specimen warming for heat-etching of fracture faces. We have now tested the Mass. General Hospital version of the Type II device (called the “Type II-MGH device”) on a wide variety of biological specimens and have established temperature and pressure curves for routine heat-etching with the device.

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