scholarly journals Variable Stars and Evolution in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 187-195
Author(s):  
Pierre Demarque
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
The Past ◽  
Rr Lyrae ◽  
Lyrae Stars ◽  
Distance Indicators

Traditionally, cluster variables have been used as distance indicators and have in this sense played an important role in our understanding of stellar evolution. In particular, the determination of the distance moduli of globular clusters and of the absolute magnitude of the main sequence turnoff, thus yielding the ages of the cluster, have relied heavily in the past on observations of RR Lyrae stars.

scholarly journals On the Existence of Luminosity Differences between HB Field and Cluster Stars

2000 ◽  
Vol 176 ◽  
pp. 265-265
Author(s):  
E. Carretta ◽  
R. G. Gratton ◽  
G. Clementini
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Distance Scale ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Intrinsic Difference ◽  
General Field ◽  
Lyrae Stars

AbstractThe discrepancy between the long distance scale as derived, e.g., from Hipparcos-based distances to globular clusters via main sequence fitting to local subdwarfs, and the short distance scale as derived, e.g., from the absolute magnitude of field RR Lyrae stars via statistical parallaxes and the Baade–Wesselink method, could be accounted for if an intrinsic difference in luminosity of about 0.1−0.2 mag were found to exist between horizontal branch (HB) stars populating the sparse general field and the dense globular clusters.

scholarly journals General Properties of the Two Groups of Globular Clusters and Their Variable Stars

1975 ◽  
Vol 67 ◽  
pp. 541-543
Author(s):  
A. V. Mironov ◽  
N. N. Samus'
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
General Properties ◽  
Rr Lyrae ◽  
Lyrae Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

scholarly journals Search for Variables in the Galactic Globular Clusters NGC 6544 and NGC 6642

1993 ◽  
Vol 139 ◽  
pp. 337-337
Author(s):  
Martha L. Hazen
Keyword(s):  
Globular Clusters ◽  
Slow Variable ◽  
Variable Stars ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
A Value ◽  
Short Period ◽  
Period Variable ◽  
Lyrae Stars

A search for variable stars in the globular cluster NGC 6544 has revealed only one possible short period variable within the tidal radius of the cluster. A search in NGC 6642 yielded 16 new RR Lyrae stars within the tidal radius and 5 new field RRs. The previously discovered (Hoffleit 1972) V1 is a slow variable, and V2 is an RR Lyrae star. Photometry of the variables within the tidal radius gives a mean B for the horizontal branch of < B > = 17.0 mag. With E(B – V) = 0.37 mag and (B – V) = 0.35 mag for RR Lyraes, a value for V(HB) = 16.3 mag is derived. This is about one mag fainter than previous estimates (Webbink 1985), and places NGC 6642 at a distance of approximately 7.9 kpc.

scholarly journals RR Lyrae stars as probes of the Milky Way structure and formation

2015 ◽  
Vol 11 (S317) ◽  
pp. 116-119
Author(s):  
Pawel Pietrukowicz ◽  
Keyword(s):  
Galactic Center ◽  
Variable Stars ◽  
Wide Field ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Galaxy ◽  
First Results ◽  
Formation And Evolution ◽  
Lyrae Stars ◽  
Distance Indicators

AbstractRR Lyrae stars being distance indicators and tracers of old population serve as excellent probes of the structure, formation, and evolution of our Galaxy. Thousands of them are being discovered in ongoing wide-field surveys. The OGLE project conducts the Galaxy Variability Survey with the aim to detect and analyze variable stars, in particular of RRab type, toward the Galactic bulge and disk, covering a total area of 3000 deg2. Observations in these directions also allow detecting background halo variables and unique studies of their properties and distribution at distances from the Galactic Center to even 40 kpc. In this contribution, we present the first results on the spatial distribution of the observed RRab stars, their metallicity distribution, the presence of multiple populations, and relations with the old bulge. We also show the most recent results from the analysis of RR Lyrae stars of the Sgr dwarf spheroidal galaxy, including its center, the globular cluster M54.

scholarly journals Turnoffs and Ages of Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 635-636
Author(s):  
F. Buonanno ◽  
C. E. Corsi ◽  
F. Fusi Pecci
Keyword(s):  
Globular Clusters ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Absolute ◽  
The Difference ◽  
Absolute Magnitudes ◽  
Lyrae Stars ◽  
The Way

The way to arrive at (even relative) ages for globular clusters involves the determination of their (relative) distances. We would like to see a theory which would fit the absolute magnitudes of RR Lyrae stars as determined from observations (Sandage effect). We have examined a sample of 17 CM diagrams of galactic globular clusters, 11 of which were observed at ESO and reduced with the program, ROMAFOT and 6 of which were taken from the literature. In Fig. 1 the difference in bolometric magnitude between the turnoff point and the location of the zero-age horizontal branch (ZAHB), δV RRTO (bo1) is plotted versus [Fe/H]. It turns out that δV RRTO ≃ δ RRTO (bo1) + 0.1 = 3.56 ±0.15. We are faced with the problem of determining how the horizontal branch scales with metallicity in order to understand the constant value of 3.56 in this relation.

Milky Way’s structure based on thousands of Cepheids and RR Lyrae stars from OGLE

2019 ◽  
Vol 14 (S353) ◽  
pp. 1-5
Author(s):  
Pawel Pietrukowicz
Keyword(s):  
Galactic Plane ◽  
Variable Stars ◽  
Thin Disk ◽  
Rr Lyrae Stars ◽  
Robust Detection ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Type Variable ◽  
Lyrae Stars ◽  
Distance Indicators

AbstractClassical Cepheids and RR Lyrae-type variable stars are widely-used tracers of young (< 300 Myr) and old (> 10 Gyr) stellar populations, respectively. These stars also serve as distance indicators allowing for Galactic structure studies. Robust detection of pulsating variables requires precise and relatively frequent observations over several years. Recently, the OGLE survey has discovered nearly 1,300 new genuine classical Cepheids and 15,000 RR Lyrae stars along the southern Galactic plane. Here, we present the picture of the Milky Way’s thin disk drawn with the Cepheids and the view of the Galactic old population that emerges from the set of known RR Lyrae stars.

scholarly journals Cepheid Pulsation Theory and Multiperiodic Cepheid Variables

1976 ◽  
Vol 29 ◽  
pp. 115-131
Author(s):  
A. N. Cox ◽  
J. P. Cox
Keyword(s):  
Variable Stars ◽  
Radial Pulsation ◽  
Rr Lyrae Stars ◽  
The Third ◽  
The Past ◽  
Rr Lyrae ◽  
Cepheid Variables ◽  
Theory Calculation ◽  
Lyrae Stars ◽  
Radial Pulsations

In this review of the situation with regard to the multiperiodic Cepheid variables, our subject matter is divided into four parts. The first discusses general causes of pulsation of Cepheids and other variable stars, and their locations on the H-R diagram. For this section we draw upon the work during the past 10-15 years of J. P. Cox, Baker, Kippenhahn, A. N. Cox, King, Christy, Castor, Stobie, Stellingwerf, Davey, Iben, and Tuggle, mostly with the small amplitude linear nonadiabatic radial pulsation theory. In the second section we review the linear adiabatic and nonadiabatic theory calculation of radial pulsation periods and their application to the problem of masses of double-mode Cepheids. Contributions discussed are by Cogan, J. P. Cox, King, Stellingwerf, Petersen, Hansen, and Ross. Periodic solutions, and their stability, of the nonlinear radial pulsation equations for Cepheids and RR Lyrae stars are considered in the third section. This research has been done by Stellingwerf with previous development of methods by Baker and von Sengbusch and current work by A. N. Cox and Davey at Los Alamos. In the last section we give the latest results on nonlinear, nonperiodic, radial pulsations for Cepheids and RR Lyrae stars. This work has been done by Stellingwerf, King, A. N. Cox, J. P. Cox, and Davey.

scholarly journals Observational Aspects of RR Lyrae Variables in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 51-67 ◽  
Author(s):  
L. Rosino
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Good Test ◽  
Rr Lyrae Stars ◽  
Pulsating Stars ◽  
Rr Lyrae ◽  
Powerful Means ◽  
The Galaxy ◽  
Points Of View ◽  
Lyrae Stars

RR Lyrae variables play a prominent role in many of the problems of globular clusters, and from several points of view. In the first place they can be considered as pretty good indicators of population and distance; although they do not form a completely homogeneous set of stars, the knowledge of their mean absolute magnitude gives a powerful means of establishing distances within and outside the Galaxy, and hence of determining the form and size of the Galaxy itself. Moreover, the number of RR Lyrae stars in clusters, the relative frequency of RRc and RRab, types, the length of the transition periods, the array of colors, when correctly interpreted, give important information on the degree of evolution, age and chemical composition of the clusters. Placed as they are in a peculiar region of the H — R diagram of Population II, the RR Lyr variables can be used as a good test of the theories of advanced evolution or the models of pulsating stars.

scholarly journals The LMC Globular Cluster Hodge 11 (=SL 868)

1984 ◽  
Vol 108 ◽  
pp. 43-44
Author(s):  
L. L. Stryker ◽  
J. M. Nemec ◽  
J. E. Hesser ◽  
R.D. McClure
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Cluster ◽  
Open Clusters ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Lyrae Stars ◽  
Termination Point

The age of the star cluster H11 has been controversial for a number of years. The color-magnitude diagram (CMD) of Walker (1979) to V=21.5 was interpreted as an “…evolved main-sequence, whose termination point corresponds to an age of about 0.6 Gyr, but with a giant branch which is displaced blueward by about Δ (B-V)o=0.4 from the positions of the giant branches of open clusters of similar age in our Galaxy.” On the other hand, the integrated colors are similar to those of metal-poor globular clusters in the Galaxy (Freeman and Gascoigne 1977, and references therein), and “…incompatible with an age of say 0.3 Gyr.” Searle, Wilkinson and Bagnuolo (1980) classify it as Group VII, the oldest group. The system has no RR Lyrae stars (Graham and Nemec 1984).

The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale

1989 ◽  
Vol 111 ◽  
pp. 255-255
Author(s):  
G. Clementini ◽  
C. Cacciari
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Absolute Magnitude ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Visual Magnitude ◽  
Phase Range ◽  
The Absolute ◽  
Lyrae Stars ◽  
Magnitude Difference

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, & Latham, 1988, preprint; Jameson, Fernley, & Longmore 1987, in press M.N.R.A.S; Cohen & Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.

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