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

Rozyczka M., Pych W., Thompson I. B., Mazur B.

Acta Astronomica

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2020

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Vol. 70, No. 4

291--299

EN

We report the detection of 20 new variables in the field of NGC 3201. Among them there are 15 confirmed cluster members. Follow-up observations are desirable for two blue stragglers with variable light curves (probably resulting from magnetic activity), and for a yellow straggler coinciding with a Chandra X-ray source. Two of the eclipsing binaries, newly detected at the turnoff in cluster's CMD, and an eclipsing binary on the red giant branch, are potentially suitable for the determination of age and distance of NGC 3201.

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The Cluster AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M10

Rozyczka M., Narloch W., Schwarzenberg-Czerny A., Thompson I. B., Poleski R., Pych W.

Acta Astronomica

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2018

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Vol. 68, No. 3

237--258

EN

The field of the globular cluster M10 (NGC 6254) was monitored between 1998 and 2015 in a search for variable stars. V-band light curves were derived for 40 variables or likely variables, most of which are new detections. Proper motions obtained within the CASE project indicate that 18 newly detected variables and 14 previously known ones are members or likely members of the cluster, including one RRc-type, three type II Cepheids, and 14 SX Phe-type pulsators, one contact binary, and six semi-regular red giants. As a by-product of the search we discovered a candidate binary comprised of main sequence stars with the record-short orbital period of 0.042 d. We also confirmed the photometric variability of the red straggler M10-VLA1 hinted at by Shishkovsky, who discovered this object spectroscopically. In Appendix 1 we show that CASE proper motion measurements are in a good agreement with those retrieved from the Gaia archive, while Appendix 2 presents evidence for low frequency γ Dor-type oscillations in SX Phe stars belonging to M10.

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The Cluster AgeS Experiment (CASE). Detecting Aperiodic Photometric Variability with the Friends of Friends Algorithm

Rozyczka M., Narloch W., Pietrukowicz P., Thompson I. B., Pych W., Poleski R.

Acta Astronomica

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2018

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Vol. 68, No. 1

63--78

EN

We adapt the friends of friends algorithm to the analysis of light curves, and show that it can be succesfully applied to searches for transient phenomena in large photometric databases. As a test case we search OGLE-III light curves for known dwarf novae. A single combination of control parameters allows us to narrow the search to 1% of the data while reaching a ≈90% detection efficiency. A search involving ≈2% of the data and three combinations of control parameters can be significantly more effective - in our case a 100% efficiency is reached. The method can also quite efficiently detect semi-regular variability. In particular, 28 new semi-regular variables have been found in the field of the globular cluster M22, which was examined earlier with the help of periodicity-searching algorithms.

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The Cluster AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M22

Rozyczka M., Thompson I. B., Pych W., Narloch W., Poleski R., Schwarzenberg-Czerny A.

Acta Astronomica

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2017

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Vol. 67, No. 3

203--224

EN

The field of the globular cluster M22 (NGC 6656) was monitored between 2000 and 2008 in a search for variable stars. BV light curves were obtained for 359 periodic, likely periodic, and long-term variables, 238 of which are new detections. 39 newly detected variables, and 63 previously known ones are members or likely members of the cluster, including 20 SX Phe, 10 RRab and 16 RRc type pulsators, one BL Her type pulsator, 21 contact binaries, and 9 detached or semi-detached eclipsing binaries. The most interesting among the identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a β Lyr type binary on the blue horizontal branch, V129 - a blue/yellow straggler with a W UMa-like light curve, located halfway between the extreme horizontal branch and red giant branch, and V134 - an extreme horizontal branch object with P=2.33 d and a nearly sinusoidal light curve. All four of them are proper motion members of the cluster. Among nonmembers, a P=2.83 d detached eclipsing binary hosting a δ Sct type pulsator was found, and a peculiar P=0.93 d binary with ellipsoidal modulation and narrow minimum in the middle of one of the descending shoulders of the sinusoid. We also collected substantial new data for previously known variables. In particular we revise the statistics of the occurrence of the Blazhko effect in RR Lyr type variables of M22.

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The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster NGC 362

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

Acta Astronomica

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2016

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Vol. 66, No. 3

307--332

EN

The field of the globular cluster NGC 362 was monitored between 1997 and 2015 in a search for variable stars. BV light curves were obtained for 151 periodic or likely periodic variable stars, over a hundred of which are new detections. Twelve newly detected variable stars are proper-motion members of the cluster: two SX Phe and two RR Lyr pulsators, one contact binary, three detached or semi-detached eclipsing binaries, and four spotted variable stars. The most interesting objects among these are the binary blue straggler V20 with an asymmetric light curve, and the 8.1 d semidetached binary V24 located on the red giant branch of NGC 362, which is a Chandra X-ray source. We also provide substantial new data for 24 previously known variable stars.

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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.

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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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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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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.