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 Spectroscopy of Overluminous Cepheids in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 223-224
Author(s):  
Horace A. Smith ◽  
Leo Connolly
Keyword(s):  
Globular Cluster ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Small Magellanic Cloud ◽  
Single Star ◽  
Rr Lyrae ◽  
Short Period ◽  
The Galaxy

The Small Magellanic Cloud is known to contain types of short period Cepheid variable stars not yet discovered in either the Large Magellanic Cloud or, with the exception of a single star, in the Galaxy. These variables can be divided into two categories: anomalous Cepheids and Wesselink-Shuttleworth (WS) stars. The former, which have also been found in dwarf spheroidal systems and in the globular cluster NGC 5466, have periods of 0.4–3 days, but average 0.7–1.0 mag. brighter than RR Lyrae and BL Her stars of equal period. The stars we call WS stars have periods less than about 1.1 day and, at MV = −1 to −2, are brighter than anomalous Cepheids of equal period.

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 The ACS LCID project: Variable stars as tracers of population gradients

2008 ◽  
Vol 4 (S258) ◽  
pp. 73-80
Author(s):  
Edouard J. Bernard ◽  
Keyword(s):  
Theoretical Models ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Short Period ◽  
History Of ◽  
Period Variable ◽  
Star Formation Histories ◽  
Lyrae Stars

AbstractWe present a few highlights concerning the search for short-period variable stars in four galaxies, namely IC 1613, LGS3, Cetus and Tucana, based on very deep, multi-epoch HST/ACS photometry. These are discussed in the context of the star formation histories obtained from our very deep color-magnitude diagrams. In particular, we show how the pulsational properties of the RR Lyrae stars, which represent the vast majority of the observed variables, can trace subtle differences in the age and metallicity of the old population. For example, in the dwarf spheroidal galaxy Tucana we find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longer period RR Lyrae variables. Through comparison with the predictions of theoretical models of stellar evolution and stellar pulsation, we interpret the fainter RR Lyrae stars as a more metal-rich subsample. In addition, we show that they must be older than about 10 Gyr, indicating that the metallicity gradient must have appeared very early on in the history of this galaxy. We also compare the populations of Cepheids in the galaxies of our sample based on their period-Wesenheit diagram. We tentatively classify them as classical short-period Cepheids in the two gas-rich galaxies (IC 1613 & LGS3), and as anomalous Cepheids in the dwarf spheroidals.

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 CCD Photometry of RR Lyrae Stars in NGC 6388 and M15

1993 ◽  
Vol 139 ◽  
pp. 338-338
Author(s):  
N.A. Silbermann ◽  
H.A. Smith ◽  
M. Bolte
Keyword(s):  
Globular Clusters ◽  
Variable Stars ◽  
Ccd Photometry ◽  
Rr Lyrae Stars ◽  
Preliminary Results ◽  
Rr Lyrae ◽  
Lyrae Stars

AbstractWe present preliminary results of a program of CCD photometry of RR Lyrae variable stars in the globular clusters NGC 6388 and M15.

scholarly journals RR Lyrae and Short-Period Variable Stars in the Dwarf Irregular Galaxy NGC 6822

2003 ◽  
Vol 588 (2) ◽  
pp. L85-L88 ◽  
Author(s):  
Gisella Clementini ◽  
Enrico V. Held ◽  
Lara Baldacci ◽  
Luca Rizzi
Keyword(s):  
Variable Stars ◽  
Irregular Galaxy ◽  
Rr Lyrae ◽  
Short Period ◽  
Period Variable ◽  
Ngc 6822

scholarly journals NGC 6822: short period variable stars, stellar population and distance scale

2004 ◽  
Vol 193 ◽  
pp. 91-94 ◽  
Author(s):  
Lara Baldacci ◽  
Luca Rizzi ◽  
Gisella Clementini ◽  
Enrico V. Held
Keyword(s):  
Stellar Population ◽  
Variable Stars ◽  
Irregular Galaxy ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Short Period ◽  
Period Variable ◽  
Ngc 6822 ◽  
Lyrae Stars

AbstractResults are presented on a study of the short period variable stars in the dwarf irregular galaxy NGC 6822. We observed an almost uniformly populated classical instability strip from the Horizontal Branch up to the Classical Cepheid region. The main goal we achieved from the analysis of the faint sample is the first detection of RR Lyrae stars in this galaxy.

scholarly journals The RR Lyrae Variables in M54 and the Sgr Dwarf Galaxy

2002 ◽  
Vol 207 ◽  
pp. 168-170
Author(s):  
C. Cacciari ◽  
M. Bellazzini ◽  
S. Colucci
Keyword(s):  
Recent Work ◽  
Globular Cluster ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Ccd Photometry ◽  
Rr Lyrae ◽  
Red Giant

We report on new B, V and I CCD photometry of the globular cluster M54 that was aimed at the study of its variable stars. With respect to the previous most recent work on M54 we have nearly doubled the number of detected variable stars: M54 can now be classified as intermediate in the Oosterhoff groups. The metallicity can be estimated for the cluster and field red giant stellar population, and for the variables.

scholarly journals Distance scale, variable stars and stellar populations in Local Group galaxies

2004 ◽  
Vol 193 ◽  
pp. 60-64 ◽  
Author(s):  
G. Clementini ◽  
L. Baldacci ◽  
A. Bragaglia ◽  
E. Carretta ◽  
L. Di Fabrizio ◽  
...  
Keyword(s):  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Short Period ◽  
Scale Variable ◽  
Period Variable ◽  
Ngc 6822 ◽  
First Time ◽  
Lyrae Stars

AbstractWe present an overview of our study of the short period variable stars in the Large Magellanic Cloud, and in the dwarf galaxies Fornax, Leo I, and NGC 6822. Light curves are presented for RR Lyrae stars, Anomalous Cepheids and, for the first time, for Dwarf Cepheids in the field and in the globular cluster #3 of the Fornax galaxy.

Sign in / Sign up

Export Citation Format

Share Document