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The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster NGC~3201

Kaluzny J., Rozyczka M., Thompson I. B., Narloch W., Mazur B., Pych W., Schwarzenberg-Czerny A.

Acta Astronomica

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2016

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Vol. 66, No. 1

31--53

EN

The field of the globular cluster NGC 3201 was monitored between 1998 and 2009 in a search for variable stars. BV light curves were obtained for 152 periodic or likely periodic variables, fifty-seven of which are new detections. Thirty-seven newly detected variables are proper motion members of the cluster. Among them we found seven detached or semi-detached eclipsing binaries, four contact binaries, and eight SX Phe pulsators. Four of the eclipsing binaries are located in the turnoff region, one on the lower main sequence and the remaining two slightly above the subgiant branch. Two contact systems are blue stragglers, and another two reside in the turnoff region. In the blue straggler region a total of 266 objects were found, of which 140 are proper motion (PM) members of NGC 3201, and another nineteen are field stars. Seventy-eight of the remaining objects for which we do not have PM data are located within the half-light radius from the center of the cluster, and most of them are likely genuine blue stragglers. Four variable objects in our field of view were found to coincide with X-ray sources: three chromospherically active stars and a quasar at a redshift z≈0.5.

2

The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M12

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

Acta Astronomica

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2015

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Vol. 65, No. 3

267--282

EN

The field of the globular cluster M12 (NGC 6218) was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for thirty-six periodic or likely periodic variable stars. Thirty-four of these are new detections. Among the latter we identified twenty proper-motion members of the cluster: six detached or semi-detached eclipsing binaries, five contact binaries, five SX Phe pulsators, and three yellow stragglers. Two of the eclipsing binaries are located in the turnoff region, one on the lower main sequence and the remaining three among the blue stragglers. Two contact systems are blue stragglers, and the remaining three reside in the turnoff region. In the blue straggler region a total of 103 objects were found, of which 42 are proper motion members of M12, and another four are field stars. 55 of the remaining objects are located within two core radii from the center of the cluster, and as such they are likely genuine blue stragglers. We also report the discoveries of a radial color gradient of M12, and the shortest period among contact systems in globular clusters in general.

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The Clusters AgeS Experiment (CASE). VI. Analysis of Two Detached Eclipsing Binaries in the Globular Cluster M55

Kaluzny J., Thompson I. B., Dotter A., Rozyczka M., Pych W., Rucinski S. M., Burley G. S.

Acta Astronomica

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2014

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Vol. 64, No. 1

11--26

EN

We present an analysis of the detached eclipsing binaries V44 and V54 belonging to the globular cluster M55. For V54 we obtain the following absolute parameters: Mp=0.726±0.015 Msun, Rp=1.006± 0.009 Rsun, Lp=1.38±0.07 Lsun for the primary, and Ms=0.555± 0.008 Msun, Rs=0.528±0.005 Rsun, Ls=0.16±0.01 Lsun for the secondary. The age and apparent distance modulus of V54 are estimated at 13.3-14.7 Gyr and 13.94±0.05 mag, respectively. This derived age is substantially larger than ages we have derived from the analysis of binary systems in 47 Tuc and M4. The secondary of V44 is so weak in the optical domain that only mass function and relative parameters are obtained for the components of this system. However, there is a good chance that the velocity curve of the secondary could be derived from near-IR spectra. As the primary of V44 is more evolved than that of V54, such data would impose much tighter limits on the age and distance of M55.

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The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Open Cluster NGC 6253

Kaluzny J., Rozyczka M., Pych W., Thompson I. B.

Acta Astronomica

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2014

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Vol. 64, No. 2

77--88

EN

The field of the metal-rich open cluster NGC 6253 has been surveyed in a search for variable stars. A total of 25 new variables were detected, 14 of which are bright stars with 13

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The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster NGC 6362

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

Acta Astronomica

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2014

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Vol. 64, No. 4

309--322

EN

The field of the globular cluster NGC 6362 was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for 69 periodic variable stars including 34 known RR Lyr stars, 10 known objects of other types and 25 newly detected variable stars. Among the latter we identified 18 proper-motion members of the cluster: seven detached eclipsing binaries (DEBs), six SX Phe stars, two W UMa binaries, two spotted red giants, and a very interesting eclipsing binary composed of two red giants - the first example of such a system found in a globular cluster. Five of the DEBs are located at the turnoff region, and the remaining two are redward of the lower main sequence. Eighty-four objects from the central 9×9 arcmin2 of the cluster were found in the region of cluster blue stragglers. Of these 70 are proper motion (PM) members of NGC 6362 (including all SX Phe and two W UMa stars), and five are field stars. The remaining nine objects lacking PM information are located at the very core of the cluster, and as such they are likely genuine blue stragglers.

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The Clusters AgeS Experiment (CASE). Analysis of the Detached Eclipsing Binary V15 in the Metal-Rich Open Cluster NGC 6253

Rozyczka M., Kaluzny J., Thompson I. B., Dotter A., Pych W., Narloch W.

Acta Astronomica

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2014

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Vol. 64, No. 3

233--246

EN

We present the first detailed analysis of the detached eclipsing binary V15 in the super-metal rich open cluster NGC 6253. We obtain the following absolute parameters: Mp=1.303±0.006 MSun, Rp=1.71±0.03 RSun, Lp=2.98±0.10 LSun for the primary, and Ms=1.225±0.006 MSun, Rs=1.44±0.02 RSun, Ls=2.13±0.06 LSun for the secondary. Based on Dartmouth isochrones, the age of NGC 6253 is estimated to be 3.80-4.25 Gyr from the mass-radius diagram and 3.9-4.6 Gyr from color-magnitude diagram fitting. Both of these estimates are significantly higher than those reported so far. The derived apparent distance modulus of 11.65 mag agrees well with the range of 10.9-12.2 mag derived by other authors; however our estimated reddening (0.113 mag) is lower than the lowest published value (0.15 mag). We confirm earlier observations that model atmospheres are not accurate enough to account for the whole CMD of the cluster, with the largest discrepancies appearing on the subgiant and giant branches. Although age estimation from the mass-radius diagram is a relatively safe, distance- and reddening-independent procedure, our results should be verified by photometric and spectroscopic observations of additional detached eclipsing binaries which we have discovered, at least two of which are proper-motion members of NGC 6253.

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The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster M4

Kaluzny J., Thompson I. B., Rozyczka M., Krzeminski W.

Acta Astronomica

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2013

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Vol. 63, No. 2

181--201

EN

Based on over 3000 BV images of M4 collected in years 1995-2009 we obtain light curves of 22 variables, 10 of which are newly detected objects. We identify four detached eclipsing binaries and eight contact binaries. Accurate periods are found for all but two variables. Nineteen variables are proper-motion members of the cluster, and the remaining three are field stars. Five variables are optical counterparts of X-ray sources. For one of the variables unassociated with X-ray sources we report a flare lasting for about 90 min and reaching an amplitude of ΔV=0.11 mag. One of the new contact binaries has a record-low mass ratio q=0.06. Another four such systems show season-to-season luminosity variations probably related to magnetic activity cycles, whose lengths are surprisingly similar to that of the solar cycle despite a huge difference in rotational periods. The location of contact binaries on the color-magnitude diagram of M4 strongly suggests that at least in globular clusters the principal factor enabling EW systems to form from close but detached binaries is stellar evolution. We identify 46 blue and yellow stragglers in M4 and discuss their properties. We also derive a map of the differential extinction in the central part of M4, and determine the reddening of a selected reference region, E(B-V)=0.392 mag.

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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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The Clusters AgeS Experiment (CASE): The Blue Straggler Star M55-V60 Caught Amidst Rapid Mass Exchange

Rozyczka M., Kaluzny J., Thompson I. B., Rucinski S. M., Pych W., Krzeminski W.

Acta Astronomica

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2013

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Vol. 63, No. 1

67--78

EN

We analyze light and velocity curves of the eclipsing blue straggler V60 in the field of the globular cluster M55. We derive Mp=1.259± 0.025 Msun, Rp=1.102±0.021 Rsun, M bolp=3.03±0.09 mag for the primary and Ms=0.327±0.017 Msun, Rs=1.480±0.011 Rsun, Mbols=4.18±0.12 mag for the secondary. We measure an apparent distance modulus (m-M)V=14.04±0.09 mag. Based on the systemic velocity, distance, and proper motion of V60 we conclude that the system is a member of the cluster and argue that its present state is a result of rapid but conservative mass exchange which the binary is still undergoing. We report a peculiar blue excess on the ascending branch of the primary eclipse of V60 and discuss its possible origin.

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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.

12

Variable Stars in the Globular Cluster NGC 6752

Kaluzny J., Thompson I. B.

Acta Astronomica

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2009

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Vol. 59, No. 3

273--289

EN

We report time-series photometry for 16 variable stars located in the central part of the globular cluster NGC 6752. The sample includes 13 newly identified objects. The precision of our differential photometry ranges from 1 mmag at V=14.0 mag to 10 mmag at V=18.0 mag. We detected four low amplitude variables located on the extended horizontal branch (EHB) of the cluster. They are candidate binary stars harboring sdB subdwarfs. A candidate degenerate binary was detected about 2 mag below the faint end of the EHB. The star is blue and its light curve is modulated with a period of 0.47 d. We argue that some of the identified variable red/blue stragglers are ellipsoidal binaries harboring degenerate stars. They have low amplitude sine-like light curves and periods from a few hours to a few days. Spectroscopic observations of such objects may lead to the detection of detached inactive binaries harboring stellar mass black holes or neutron stars. No binaries of this kind are known so far in globular clusters although their existence is expected based on the common occurrence of accreting LMXBs and millisecond pulsars. An eclipsing SB1 type binary was identified on the upper main sequence of the cluster. We detected variability of optical counterparts to two X-ray sources located in the core region of NGC 6752. The already known cataclysmic variable B1=CX4 experienced a dwarf nova type outburst. The light curve of an optical counterpart to the X-ray source CX19 exhibited modulation with a period of 0.113 d. The same periodicity was detected in the HST-ACS data. The variable is located on the upper main sequence of the cluster. It is an excellent candidate for a close degenerate binary observed in quiescence.

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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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A New Lower Main Sequence Eclipsing Binary with Detached Components

Rozyczka M., Kaluzny J., Pietrukowicz P., Pych W., Mazur B., Catelan M., Thompson I. B.

Acta Astronomica

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2009

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Vol. 59, No. 4

385--401

EN

We present an analysis of NGC2204-S892 - a new detached eclipsing binary composed of two late K dwarfs. Based on three photometric campaigns launched in 2008 we obtained five light curves (three in V, one in B and one in I), and derived an orbital period. We also obtained 20 VLT/UVES spectra, enabling accurate radial velocity measurements. The derived masses and radii of the components are consistent with the empirical mass-radius relationship established recently for lower main sequence stars in binary systems; in particular we find that both stars are oversized compared to theoretical models. NGC2204-S892 is very active: both components show variable emission in Hα and Hβ and are heavily spotted, causing the light curve to show appreciable changes on a timescale of weeks. Our results add to the increasing evidence that the observed inflation of the radii of K and M stars is related to high levels of magnetic activity.

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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.

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Variable Stars in the Field of the Open Cluster NGC 2204

Rozyczka M., Kaluzny J., Krzeminski W., Mazur B.

Acta Astronomica

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2007

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Vol. 57, No. 4

323--329

EN

We present the results of a variable stars search in the field of the old open cluster NGC 2204. Five new variables were found, four of them being eclipsing binaries. The sample includes a detached binary located at the turnoff, a W UMa - type system, and an interesting detached low-mass binary with a period of 0.45 d which, however, is a foreground object. We provide V-light curves and finder charts for all variables together with color-magnitude diagrams of the cluster. For four variables incomplete I-light curves are also provided.

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Eclipsing Binaries in the Open Cluster NGC 2243. II. Absolute Properties of NVCMa

Kaluzny J., Pych W., Rucinski S. M., Thompson I. B.

Acta Astronomica

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2006

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Vol. 56, No. 3

237--252

EN

We present echelle spectroscopic data for five eclipsing binary stars and two giant stars in the field of the open cluster NGC 2243. The average cluster velocity is determined to be +60.4±0.6 km/s. Four of the eclipsing binaries are very likely members of the cluster based on their observed radial velocities. The absolute parameters of cluster member NV CMa are determined by analyzing photometric and radial velocity data. We obtain 1.089±0.010 Msolar and 1.221±0.031 Rsolar for the primary, and 1.069±0.010 Msolar and 1.178±0.037 Rsolar for the secondary. Both components of the binary are located on the Main Sequence, about 1 mag below the turn-off point on the cluster color-magnitude diagram. Using model age-luminosity and age-radius relations we obtain 4.35±0.25 Gyr for the age of NV CMa. The derived age is, however, very sensitive to the adopted metallicity of the cluster. We demonstrate that a meaningful determination of the ages of objects like NV CMa based on evolutionary models is possible only if their metallicity is known with a relative accuracy of a few percent. The distance moduli calculated for the components of NV CMa agree closely with each other, and imply an apparent distance modulus of the cluster of (m-M)V=13.24±0.08 mag.

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Eclipsing Binaries in the Open Cluster NGC 2243 - I. Photometry

Kaluzny J., Krzeminski W., Thompson I. B., Stachowski G.

Acta Astronomica

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2006

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Vol. 56, No. 1

51--63

EN

We obtained BV time series photometry for 12 variable stars from the field of the old open cluster NGC 2243. The sample includes 3 newly identified detached/semi-detached binaries. There are now four detached eclipsing binaries which are likely members of the cluster. Determination of the absolute parameters of the components would provide a valuable check on evolutionary models of low-mass stars. An accurate ephemeris and orbital period analysis are presented for the previously-known detached binary NV CMa. We also provide ephemerides for seven other periodic variables. We show that three contact binaries are likely members of the cluster.

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Cluster AgeS Experiment (CASE): Dwarf Novae and a Probable Microlensing Event in the Globular Cluster M22

Pietrukowicz P., Kaluzny J., Thompson I. B., Jaroszyński M., Schwarzenberg-Czerny A., Krzeminski W., Pych W.

Acta Astronomica

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2005

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Vol. 55, No. 3

261--274

EN

We report the identification of a new cataclysmic variable (denoted as CV2) and a probable microlensing event in the field of the globular cluster M22. Two outbursts were observed for CV2. During one of them superhumps with Psh=0.08875 d were present in the light curve. CV2 has an X-ray counterpart detected by XMM-Newton. A very likely microlensing event at a radius of 2.'3 from the cluster center was detected. It had an amplitude of Δ V=0.75 mag and a characteristic time of 15.9 days. Based on model considerations we show that the most likely configuration has the source in the Galactic bulge with the lens in the cluster. Two outbursts were observed for the already known dwarf nova CV1.