scholarly journals A Study of Double- and Multi-mode RR Lyrae Variables

2015 ◽  
Vol 24 (4) ◽  
Author(s):  
A. V. Khruslov
Keyword(s):  
Globular Clusters ◽  
Variable Stars ◽  
B Stars ◽  
Galactic Field ◽  
Rr Lyrae ◽  
Period Distribution ◽  
Evolution Stage ◽  
Multi Mode ◽  
Radial Pulsations

AbstractWe present the results of our new study of known RR Lyrae variable stars. All observations available for these stars in the Catalina Surveys were analyzed, and double-mode variations were identified. We studied the Petersen diagram and the period distribution for the double-mode RR Lyrae variables in the Galactic field, pulsating in the first-overtone and fundamental modes. The double-peaked character of the period distribution was detected for Galactic RR(B) stars, corresponding to Oosterhoff’s classes of globular clusters, which indicates that the age and evolution stage of RR(B) stars in the field and RR Lyrae variables in globular clusters are probably the same. Besides, we discovered five RRC stars with two simultaneously excited non-radial pulsations (equidistant triplets).

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 CCD Observations of Variable Stars in Globular Clusters

1989 ◽  
Vol 111 ◽  
pp. 285-285
Author(s):  
H.A. Smith ◽  
J.R. Kuhn ◽  
J. Curtis
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Variable Stars ◽  
Michigan State University ◽  
State University ◽  
Ccd Photometry ◽  
Rr Lyrae ◽  
Short Period ◽  
Ccd Observations ◽  
Period Variable

AbstractBVR observations of the relatively metal-rich globular cluster NGC 6388 have been obtained with a CCD on the CTIO 0.9 m telescope. Eighteen possible short period variable stars have been discovered in or near the cluster. At least 10 of these are probable RR Lyrae members of NGC 6388. We confirm the finding of Hazen and Hesser that this cluster is one of the most metal-rich to contain a significant number of RR Lyraes. A program of CCD photometry of field and cluster variable stars has been initiated on the 0.6m telescope of the Michigan State University Observatory.

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 Oscillations of HB Red Variable Stars

1998 ◽  
Vol 185 ◽  
pp. 401-402
Author(s):  
D.R. Xiong ◽  
Q. L. Cheng ◽  
L. Deng
Keyword(s):  
Globular Clusters ◽  
Turbulent Viscosity ◽  
Variable Stars ◽  
Instability Strip ◽  
Rr Lyrae ◽  
Short Period ◽  
Spatial Oscillations ◽  
The Right ◽  
Thermodynamic Coupling ◽  
Low Amplitude

Using a nonlocal time-dependent theory of convection, we have calculated the linear non-adiabatic oscillations of the Horizontal Branch (HB) stars, with both the dynamic and thermodynamic coupling between convection and oscillations been carefully treated. Turbulent pressure and turbulent viscosity have been included consistently in our equations of non-adiabatic pulsation. When the coupling between convection and oscillations is ignored, for all models with Te ≤ 7350K, the fundamental through the second overtone are pulsationally unstable; while for Te ≤ 6200K all the models are unstable up to (at least) the 9th overtone. When the coupling between convection and oscillations is included, the RR Lyrae instability strip is very well predicted. Within the strip most models are pulsationally unstable only for the fundamental and the first few overtones. Turbulent viscosity is an important damping mechanism. Being exclusively distinct from the luminous red variables (long period variables), the HB stars to the right of the RR Lyrae strip are pulsationally stable for the fundamental and low-order overtones, but become unstable for some of the high-order overtones. This may provide a valuable clue for the short period, low amplitude red variables found outside the red edge of the RR Lyrae strip on the H-R diagram of globular clusters. Moreover, we present a new radiation modulated excitation mechanism functioning in radiation flux gradient regions. The effects of nonlocal convection and the dynamic coupling between convection and oscillations are discussed. The spatial oscillations of the thermal variables in the pulsational calculations have been effectively suppressed.

scholarly journals Search for variable stars in globular clusters

1986 ◽  
Vol 118 ◽  
pp. 287-288
Author(s):  
M. L. Hazen-Liller
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Variable Stars ◽  
Galactic Bulge ◽  
Rr Lyrae ◽  
High Metallicity

A program to search poorly studied southern globular clusters for variable stars is being carried out on the 1-m Yale telescope at CTIO. Recently two galactic bulge clusters of moderately high metallicity have been found to contain RR Lyrae variables; a cluster of similar metallicity a little farther from the galactic center apparently has none.

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 VISTA variable survey in the Milky Way

2009 ◽  
Vol 5 (S262) ◽  
pp. 287-290
Author(s):  
M. Hempel ◽  
D. Minniti ◽  
R. Saito ◽  
P. Pietrukowicz ◽  
P. W. Lucas
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Variable Stars ◽  
Open Clusters ◽  
Point Sources ◽  
Population Census ◽  
Cluster Evolution ◽  
Rr Lyrae ◽  
Public Survey ◽  
History Of

AbstractOver the next 5 years the VVV collaboration (Vista Variable in the Via Lactea) will conduct an extensive survey of the galactic bulge and disk in the near-IR, using the new VISTA telescope. This public survey covers a field of 520 sqr. deg, including not only regions of high star formation, but also 33 known globular clusters and ~350 open clusters. The final product will be a deep IR atlas in 5 passbands for ~109 point sources among which we expect 106 variable stars. These will be produce a 3-D map of the surveyed region using well-understood primary distance indicators such as RR Lyrae stars. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, Integral, and ALMA for a complete understanding of the variable sources in the inner Milky Way. Several important implications for the history of the Milky Way, for globular cluster evolution, for the population census of the bulge and center, and for the pulsation theory will follow from this survey.

scholarly journals Short-Period Variables in Globular Clusters of Moderate Metallicity

1988 ◽  
Vol 126 ◽  
pp. 593-594
Author(s):  
Martha L. Hazen
Keyword(s):  
Globular Clusters ◽  
Variable Stars ◽  
Rr Lyrae ◽  
Short Period ◽  
Galactic Globular Clusters

Three Galactic globular clusters of moderate metallicity, (−0.7 > [Fe/H] > −0.9), have been searched for variable stars. NGC 6388 and NGC 6569 appear to contain RR Lyrae variables as members; NGC 6652 does not. NGC 6388 and NGC 6569 thus appear to have bluer horizontal branches than normally found at their metallicity.

scholarly journals Low Amplitude New Type Variable Stars in Globular Clusters

1993 ◽  
Vol 134 ◽  
pp. 163-165
Author(s):  
Yao Bao-An ◽  
Zhang Chung-Sheng ◽  
Qin Dao ◽  
Tong Jian-Hua
Keyword(s):  
Globular Clusters ◽  
Variable Stars ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Type Variable ◽  
New Type ◽  
New Challenges ◽  
Low Amplitude

Rapid progress in the stellar pulsation research has presented many new challenges to traditional pulsation theory. The following progress made by us should belong to one of the new challenges: 1)There are many variable stars located at the Horizontal Branch (HB) but outside the instability strip with amplitude larger than 0.02 mag.Maybe some astronomers have already doubted of the 1950’s conclusion-the RR Lyrae stars are confined to the narrow instability strip in the C-M diagram, the boundaries of the gap are extremely sharp and definite, beyond the edges no light variations occur with ranges greater than 0.02 mag. We are changing the conclusion by observations. Here we do not mean the microvariability. We still raise the question from the classical viewpoint. We want to show that there are variable stars outside the strip with peak to peak amplitudes larger than 0.02 mag.

scholarly journals RR Lyrae Stars in Globular Clusters

2000 ◽  
Vol 176 ◽  
pp. 165-171
Author(s):  
Alistair R. Walker
Keyword(s):  
Globular Clusters ◽  
Stellar Populations ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
Technical Aspects ◽  
Rr Lyrae ◽  
Lyrae Stars

AbstractOf the several types of variable stars that occur in globular clusters, RR Lyrae stars have deservedly received the most attention. These stars are ideally suited for comparisons between evolution and pulsation theory, they play a prominent role in distance determinations, and are valuable tracers of the oldest stellar populations. After a brief discussion of technical aspects, we review some of the recent observational work.

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