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The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster 47 Tucanae

Kaluzny J., Rozyczka M., Pych W., Krzeminski W., Zloczewski K., Narloch W., Thompson I. B.

Acta Astronomica

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2013

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Vol. 63, No. 3

309--322

EN

Based on over 5400 BV images of 47 Tuc collected between 1998 and 2010 we obtained light curves of 65 variables, 19 of which are newly detected objects. New variables are located mostly just outside the core in a region poorly studied by earlier surveys of the cluster. Among them there are four detached eclipsing binaries and five likely optical counterparts of X-ray sources. Two detached systems are promising targets for follow-up observations. We briefly discuss properties of the most interesting new variables.

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A Proper Motion Study of the Globular Clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752

Zloczewski K., Kaluzny J., Rozyczka M., Krzeminski W., Mazur B., Thompson I. B.

Acta Astronomica

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2012

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Vol. 62, No. 4

357--375

EN

We derive relative proper motions of stars in the fields of globular clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752 based on a uniform data set collected between 1997 and 2008. We assign a membership class for each star with a measured proper motion and show that these membership classes can be successfully used to eliminate field stars from color-magnitude diagrams of the clusters. They also allow for the efficient selection of rare objects such as blue/yellow/red stragglers and stars from the asymptotic giant branch. Tables with proper motions and photometry of over 87 000 stars are made publicly available via the Internet.

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The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55

Kaluzny J., Thompson I. B., Krzeminski W., Zloczewski K.

Acta Astronomica

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2010

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Vol. 60, No. 3

245--260

EN

We report time-series photometry for 55 variable stars located in the central part of the globular cluster M55. The sample includes 28 newly identified objects of which 13 are eclipsing binaries. Three of these are detached systems located in the turn-off region on the cluster color-magnitude diagram. Two of them are proper motion (PM) members of M55 and are excellent candidates for a detailed follow-up study aimed at a determination of the cluster age and distance. Other detached binaries are located along the unevolved part of the cluster main sequence. Most of the variable stars are cluster blue straggler stars. This group includes 35 SX Phe stars, two contact binaries, and one semi-detached binary. V60 is a low mass, short period Algol with the less massive and cooler component filling its Roche lobe. The more massive component is an SX Phe variable star. The orbital period of V60 increases at a rate of dP/P=3.0×10-9. In addition to numerous variable blue stragglers we also report the detection of two red stragglers showing periodic variability. Both of these are PM members of M55. We note and discuss the observed paucity of contact binaries among unevolved main sequence stars in M55 and NGC 6752. This apparent paucity supports an evolution model in which the formation of contact binaries is triggered by stellar evolution at the main-sequence turn off.

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Photometric Survey of Stellar Clusters in the Outer Part of M33. II. Analysis of HST/ACS Images

Zloczewski K., Kaluzny J.

Acta Astronomica

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2009

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Vol. 59, No. 1

47--67

EN

We have used deep ACS/WFC images of M33 to check the nature of extended objects detected by the ground based survey of Zloczewski etal (2008). A total of 24 candidates turned out to be genuine compact stellar clusters. In addition we detected 91 new clusters. Equatorial coordinates, integrated magnitudes and angular sizes are listed for all 115 objects. Forty-two clusters have sufficiently red colors to be candidates for old globulars. For four clusters we extracted resolved stellar photometry. Object 33-3-018 located in the outer disk of M33 turned out to be a young cluster with an age estimated at 200-350 Myr. Cluster ZK-90 has an age of 3-5 Gyr. The remaining two clusters have intermediate ages ranging from one to a few Gyr.

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An Unusual Eclipsing Blue Straggler V8-NGC 6752

Kaluzny J., Rozyczka M., Thompson I. B., Zloczewski K.

Acta Astronomica

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2009

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Vol. 59, No. 4

371--383

EN

We report the analysis of a binary blue straggler in NGC 6752 with a short orbital period of 0.315 d and a W UMA-type light curve. We use photometric data spanning 13 years to place limits on the mass ratio (0.15≤q≤0.35), luminosity ratio (L1/L2≈4.0) and the ratio of the radii of the components (r1/r22≈2.0). The effective temperatures of the components are nearly identical, and the system is detached or semi-detached (in the latter case the component filling its Roche lobe is the secondary). Such a configuration is unusual given the shortness of the orbital period, and it must have resulted from substantial mass exchange. We suggest that some secondaries of W UMa-type stars, normally regarded as main sequence objects which fill their Roche lobes to different degrees, in fact may be shell-burning cores of originally more massive components.

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Photometric Survey for Stellar Clusters in the Outer Part of M33

Zloczewski K., Kaluzny J., Hartman J.

Acta Astronomica

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2008

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Vol. 58, No. 1

23--39

EN

We present a catalog of 4780 extended sources from the outer field of M33. The catalog includes 73 previously identified clusters or planetary nebulae, 1153 likely background galaxies, and 3554 new candidate stellar clusters. The survey is based on deep ground-based images obtained with the MegaCam instrument on the CFHT telescope. We provide g'r'i' photometry for detected objects as well as estimates of the FWHM and ellipticity of their profiles. The sample includes 122 new, relatively bright, likely globular clusters. Follow-up observations of fainter candidates from our list may extend the faint-end of the observed luminosity function of globular clusters in M33 by up to 3 magnitudes. The catalog includes several cluster candidates located in the outskirts of the galaxy. These objects are promising targets for deep photometry with the HST. We present a color-magnitude diagram for one detected object, showing that it is an extended and low-surface-brightness old cluster located at an angular distance of 27' from the center of M33.