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1

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VII. Classical Cepheids in the Small Magellanic Cloud

Soszyński I., Poleski R., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K.

Acta Astronomica

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2010

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Vol. 60, No. 1

17--39

EN

The seventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS) consists of 4630 classical Cepheids in the Small Magellanic Cloud (SMC). The sample includes 2626 fundamental-mode (F), 1644 first-overtone (1O), 83 second-overtone (2O), 59 double-mode F/1O, 215 double-mode 1O/2O, and three triple-mode classical Cepheids. For each object basic parameters, multi-epoch VI photometry collected within 8 or 13 years of observations, and finding charts are provided in the OGLE Internet archive. We present objects of particular interest: exceptionally numerous sample of single-mode second-overtone pulsators, five double Cepheids, two Cepheids with eclipsing variations superimposed on the pulsation light curves. At least 139 first-overtone Cepheids exhibit low-amplitude secondary variations with periods in the range 0.60-0.65 of the primary ones. These stars populate three distinct sequences in the Petersen diagram. The origin of this secondary modulation is still unknown. Contrary to the Large Magellanic Cloud (LMC) we found only a few candidates for anomalous Cepheids in the SMC. This fact may be a clue for the explanation of the origin of the anomalous Cepheids. The period and luminosity distributions of Cepheids in both Magellanic Clouds suggest that there are two or three populations of classical Cepheids in each of the galaxies. The main difference between the LMC and SMC lays in different numbers of Cepheids in each group. We fit the period-luminosity (PL) relations of SMC Cepheids and compare them with the LMC PL laws.

2

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VI. Delta Scuti Stars in the Large Magellanic Cloud

Poleski R., Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K.

Acta Astronomica

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2010

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Vol. 60, No. 1

1--16

EN

The sixth part of the OGLE-III catalog of Variable Stars presents δ Sct pulsators in the Large Magellanic Cloud. Altogether 2786 variable stars were found and amongst them 92 are multi-mode objects, including 67 stars pulsating in the fundamental mode and the first overtone (F/1O), nine double-mode pulsators with various combinations of the first three overtones excited (1O/2O, 2O/3O and 1O/3O pulsators), and two triple mode (F/1O/2O) δ Sct stars. In total 1490 of stars are marked as uncertain, due to scattered photometry and small amplitudes. For single-mode objects it was not possible to unambiguously identify pulsation mode, however we suggest the most of the single-mode variable stars pulsate in the first overtone.

3

The Araucaria Project: The Distance to the Small Magellanic Cloud from Near Infrared Photometry of Type II Cepheids

Ciechanowska A., Pietrzyński G., Szewczyk O., Gieren W., Soszyński I.

Acta Astronomica

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2010

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Vol. 60, No. 3

233--243

EN

We have obtained deep near infrared J- and K-band observations of 14 BL Her and 5 W Vir SMC stars from the OGLE-III survey with the ESO New Technology Telescope equipped with the SOFI infrared camera. From these observations, period-luminosity (P-L) relations in the J and Ks 2MASS bands were derived. The slopes of the K- and J-band relations of -2.15±0.19 and -1.95±0.24, respectively, agree very well with the corresponding slopes derived previously for population II Cepheids in globular clusters, Galactic bulge and in the Large Magellanic Cloud. The distance modulus to the SMC obtained from our data using P-L relation derived for globular cluster Cepheids equals to 18.85±0.07 (statistical) ± 0.07 mag (systematic without including potential metallicity effect), which within the uncertainties agrees well with the results obtained with other methods.

4

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. V. R Coronae Borealis Stars in the Large Magellanic Cloud

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2009

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Vol. 59, No. 4

335--347

EN

The fifth part of the OGLE-III Catalog of Variable Stars presents 23 R CrB (RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been spectroscopically confirmed by previous studies, while 6 stars are new candidates for RCB variables. We publish the VI multi-epoch OGLE photometry for all objects. We use the sample of carbon-rich long-period variables released in the previous part of this catalog to select objects with severe drops in luminosity, i.e., with the DY-Per-like light curves. DY Per stars are often related to R CrB variables. We detect at least 600 candidates for DY Per stars, mostly among dust enshrouded giants. We notice that our candidate DY Per stars form a continuity with other carbon-rich long-period variables, so it seems that DY Per stars do not constitute a separate group of variable stars.

5

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2009

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Vol. 59, No. 3

239--253

EN

The fourth part of the OGLE-III Catalog of Variable Stars presents 91 995 long-period variables (LPVs) in the Large Magellanic Cloud (LMC). This sample consists of 79 200 OGLE Small Amplitude Red Giants (OSARGs), 11 128 semiregular variables (SRVs) and 1667 Mira stars. The catalog data include basic photometric and astrometric properties of these stars, long-term multi-epoch VI photometry and finding charts. We describe the methods used for the identification and classification of LPVs. The distribution of I-band amplitudes for carbon-rich stars shows two maxima, corresponding to Miras and SRVs. Such a distinction between Miras and SRVs is not obvious for oxygen-rich stars. We notice additional period-luminosity sequence located between Wood's sequences C and C' and populated by SRVs.

6

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. III. RR Lyrae Stars in the Large Magellanic Cloud

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2009

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Vol. 59, No. 1

1--18

EN

The third part of the OGLE-III Catalog of Variable Stars comprises 24 906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17 693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode (RRd) and 1269 suspected second-overtone (RRe) pulsators. 66 objects are foreground Galactic RR Lyr stars. The catalog data include basic photometric and astrometric properties of these RR Lyr stars, multi-epoch VI photometry and finding charts. We detected one new RR Lyr star with additional eclipsing variations. The spatial distribution of RR Lyr stars in the LMC is distinctly non-spherical and it is elongated in the same direction as the LMC bar. The basic statistical features of RR Lyr stars in the LMC are provided. The apparent V-band magnitudes for RRab stars have the modal value at 19.36 mag, and for overtone RR Lyr stars it is about 19.32 mag. The mean periods for RRab, RRc and RRe stars are 0.576, 0.337 and 0.270 days, respectively.

7

The Optical Gravitational Lensing Experiment. Triple-Mode and 1O/3O Double-Mode Cepheids in the Large Magellanic Cloud

Soszyński I., Poleski R., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K.

Acta Astronomica

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2008

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Vol. 58, No. 3

153--162

EN

We report the discovery of three new triple-mode classical Cepheids in the Large Magellanic Cloud, two of them with the fundamental, first overtone and second overtone excited, and one pulsating simultaneously in the first three overtones. Thus, the number of triple-mode Cepheids in the LMC is increased to five. We also present two objects belonging probably to a new type of double-mode Cepheids having the first and third overtones excited. We measure the rates of period change in these stars and detect decrease of periods in two of them, what is in conflict with theoretical predictions.

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The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. I. Classical Cepheids in the Large Magellanic Cloud

Soszyński I., Poleski R., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K.

Acta Astronomica

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2008

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Vol. 58, No. 3

163--185

EN

We present the first part of a new catalog of variable stars (OIII-CVS) compiled from the data collected in the course of the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). In this paper we describe the catalog of 3361 classical Cepheids detected in the ≈40 square degrees area in the Large Magellanic Cloud. The sample consists of 1848 fundamental-mode (F), 1228 first-overtone (1O), 14 second-overtone (2O), 61 double-mode F/1O, 203 double-mode 1O/2O, 2 double-mode 1O/3O, and 5 triple-mode classical Cepheids. This sample is supplemented by the list of 23 ultra-low amplitude variable stars which may be Cepheids entering or exiting instability strip. The catalog data include VI high-quality photometry collected since 2001, and for some stars supplemented by the OGLE-II photometry obtained between 1997 and 2000. We provide basic parameters of the stars: coordinates, periods, mean magnitudes, amplitudes and parameters of the Fourier light curve decompositions. Our sample of Cepheids is cross-identified with previously published catalogs of these variables in the LMC. Individual objects of particular interest are discussed, including single-mode second-overtone Cepheids, multiperiodic pulsators with unusual period ratios or Cepheids in eclipsing binary systems. We discuss the variations of the Fourier coefficients with periods and point out on the sharp feature for periods around 0.35 days of first-overtone Cepheids, which can be explained by the occurrence of 2:1 resonance between the first and fifth overtones. Similar behavior at P≈3 days for 1O Cepheids and P≈10 days for F Cepheids are also interpreted as an effect of resonances between two radial modes. We fit the period-luminosity relations to our sample of Cepheids and compare these functions with previous determinations.

9

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II. Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2008

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Vol. 58, No. 4

293--312

EN

In the second part of the OGLE-III Catalog of Variable Stars (OIII-CVS) we present 197 type II Cepheids and 83 anomalous Cepheids in the Large Magellanic Cloud (LMC). The sample of type II Cepheids consists of 64 BL Her stars, 96 W Vir stars and 37 RV Tau stars. Anomalous Cepheids are divided into 62 fundamental-mode and 21 first-overtone pulsators. These are the largest samples of such types of variable stars detected anywhere outside the Galaxy. We present the period-luminosity and color-magnitude diagrams of stars in the sample. If the boundary period between BL Her and W Vir stars is adopted at 4 days, both groups differ significantly in (V-I) colors. We identify a group of 16 peculiar W Vir stars with different appearance of the light curves, brighter and bluer than ordinary stars of that type. Four of these peculiar W Vir stars show additional eclipsing modulation superimposed on the pulsation light curves. Four other stars of that type show long-period secondary variations which may be ellipsoidal modulations. It suggests that peculiar W Vir subgroup may be related to binarity. In total, we identified seven type II Cepheids simultaneously exhibiting eclipsing variations which is a very large fraction compared to classical Cepheids in the LMC. We discuss diagrams showing Fourier parameters of the light curve decomposition against periods. Three sharp features interpreted as an effect of resonances between radial modes are detectable in these diagrams for type II Cepheids.

10

The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Large Magellanic Cloud

Udalski A., Soszyński I., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski L., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2008

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Vol. 58, No. 2

89--102

EN

We present the OGLE-III Photometric Maps of the Large Magellanic Cloud. They cover about 40 square degrees of the LMC and contain mean, calibrated VI photometry and astrometry of about 35 million stars observed during seven observing seasons of the third phase of the Optical Gravitational Lensing Experiment - OGLE-III. We discuss the quality of data and present color-magnitude diagrams of selected fields. The OGLE-III Photometric Maps of the LMC are available to the astronomical community from the OGLE Internet archive.

11

The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Small Magellanic Cloud

Udalski A., Soszyński I., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K., Poleski R.

Acta Astronomica

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2008

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Vol. 58, No. 4

329--343

EN

We present OGLE-III Photometric Maps of the Small Magellanic Cloud. They contain precise, calibrated VI photometry of about 6.2 million stars from 41 OGLE-III fields in the SMC observed regularly in the years 2001-2008 and covering about 14 square degrees in the sky. Also precise astrometry of these objects is provided. One of the fields, SMC140, is centered on the 47 Tucanae Galactic globular cluster providing unique data on this object. We discuss quality of the data and present a few color-magnitude diagrams of the observed fields. All photometric data are available to the astronomical community from the OGLE Internet archive.

12

The Optical Gravitational Lensing Experiment. Variable Stars in the Field of Open Cluster NGC 6755

Ciechanowska A., Pietrzyński G., Kołaczkowski Z., Wyrzykowski Ł., Szewczyk O., Kubiak M., Udalski A., Szymański M. K.

Acta Astronomica

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2007

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Vol. 57, No. 3

249--266

EN

We present the results from a search for variable stars in the field of a young open cluster NGC 6755. Altogether seventy one variable stars have been discovered. Thirty one of them are eclipsing systems. This group contains ten EA, four EB and seventeen EW-type systems. Photometric variability of four late type stars is most probably caused by their chromospherical activity. Another seven detected variable stars have light curves typical for pulsating stars from the main instability strip. Four of them we tentatively classified as γ Dor, one as δ Sct and two as Population II Cepheid variable stars, respectively. Star designated as V40 can be either another population II Cepheid or an ellipsoidal binary system. The remaining twenty eight variable stars found in the field of this open cluster are most probably highly obscured background red giants (OSARG, irregular). For all detected variable stars we provide their light curves, preliminary classification, discussion on the possible cluster membership, equatorial coordinates, finding charts and periods when possible.

13

The Optical Gravitational Lensing Experiment. Period-Luminosity Relations of Variable Red Giant Stars

Soszyński I., Dziembowski W. A., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Ulaczyk K.

Acta Astronomica

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2007

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Vol. 57, No. 3

201--225

EN

Period-luminosity (PL) relations of variable red giants in the Large (LMC) and Small Magellanic Clouds (SMC) are presented. The PL diagrams are plotted in three planes: log P-KS, log P-WJK, and log P-WI, where WJK and WI are reddening free Wesenheit indices. Fourteen PL sequences are distinguishable, and some of them consist of three closely spaced ridges. Each of the sequences is fitted with a linear or quadratic function. The similarities and differences between the PL relations in both galaxies are discussed for four types of red giant variability: OGLE Small Amplitude Red Giants (OSARGs), Miras and Semiregular Variables (SRVs), Long Secondary Periods (LSPs) and ellipsoidal variables. We propose a new method of separating OSARGs from non-variable stars and SRVs. The method employs the position in the reddening-free PL diagrams and the characteristic period ratios of these multiperiodic variables. The PL relations for the LMC OSARG are compared with the calculated relations for RGB models along isochrones of relevant ages and metallicities. We also compare measured periods and amplitudes of the OSARGs with predictions based on the relations valid for less luminous solar-like pulsators. Miras and SRVs seem to follow PL relation of the same slopes in the LMC and SMC, while for LSP and ellipsoidal variables slopes in both galaxies are different. The PL sequences defined by LSP variables and binary systems overlap in the whole range of analyzed wavebands. We put forward new arguments for the binary star scenario as an explanation of the LSP variability and elaborate on it further. The measured pulsation to orbital period ratio implies nearly constant ratio of the star radius to orbital distance, R/A≈0.4, as we find. Combined effect of tidal friction and mass loss enhanced by the low-mass companion may explain why such a value is preferred.

14

Binary Lenses in OGLE III EWS Database. Season 2005

Skowron J., Jaroszyński M., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Szewczyk O., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2007

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Vol. 57, No. 4

281--299

EN

We present nine new binary lens candidates from OGLE-III Early Warning System database for the season of 2005. We have also found four events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses in our previous studies (10 caustic crossing events of OGLE-II seasons 1997-1999 and 34 binary lens events of OGLE-III seasons 2002-2004, including one planetary event), in this work and in three publications concerning planetary events of season 2005, we find four cases of extreme mass ratio binaries (q≤0.01), and almost all other models with mass ratios in the range 0.1

15

The Optical Gravitational Lensing Experiment. Variable Stars in the Field of Open Cluster NGC 6259

Ciechanowska A., Pietrzyński G., Wyrzykowski Ł., Szewczyk O., Kubiak M., Udalski A., Szymański M. K.

Acta Astronomica

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2006

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Vol. 56, No. 2

219--236

EN

We present the results of a search for variable stars in the field of NGC 6259. Altogether 85 variable stars have been discovered. 36 of them are eclipsing systems. This group contains 13 EA, 2 EB and 21 EW-type stars. Light curves of two variable stars resemble those of Miras. The remaining 47 variable stars detected in the field of this open cluster are most probably highly obscured red giants (OSARG, irregular). For all detected variable stars we provide their light curves, preliminary classification, discussion on the possible cluster membership, equatorial coordinates, finding charts and periods when possible.

16

The Optical Gravitational Lensing Experiment. Variable Baseline Microlensing Events in the Galactic Bulge

Wyrzykowski Ł., Udalski A., Mao S., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Szewczyk O.

Acta Astronomica

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2006

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Vol. 56, No. 2

145--169

EN

We present the first systematic search for microlensing events with variability in their baselines using data from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). A total of 137 candidates (88 new) was discovered toward the Galactic bulge. Among these, 21 have periodic oscillations in their baselines, 111 are irregular variables and 5 are potential long period detached eclipsing binaries. This is about 10% of the total number of constant baseline events. They are hence quite common and can be regarded as a new type of exotic events, which allow the determination of extra parameters of the events. We show that microlensing of variable stars may allow us to break the degeneracy between the blending parameter and magnification. We note that in some cases variability hidden in the baseline due to strong blending may be revealed in highly magnified events and resemble other exotic microlensing behavior, including planetary deviation. A new system (VEWS) for detecting ongoing variable baseline microlensing events is presented.

17

The Optical Gravitational Lensing Experiment. OGLE-III Long Term Monitoring of the Gravitational Lens QSO 2237+0305

Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł., Ulaczyk K., Więckowski T.

Acta Astronomica

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2006

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Vol. 56, No. 4

293--305

EN

We present results of the long term monitoring of the gravitational lens QSO 2237+0305 conducted during the OGLE survey. Light curves of all four components of the lens obtained during the second phase of the OGLE project (OGLE-II; 1997-2000) are supplemented with the data collected in the OGLE-III phase in the observing seasons 2001-2006. Calibration procedures to tie the new OGLE-III data with already calibrated OGLE-II light curves are described. The resulting homogeneous OGLE data set is the most extensive photometric coverage of the gravitational lens QSO 2237+0305, spanning now one decade - the seasons from 1997 to 2006 - and revealing unique microlensing activity of this spectacular object. All photometric data of the gravitational lens QSO 2237+0305 collected by OGLE are available to the astronomical community from the OGLE Internet} archive.

18

Binary Lenses in OGLE-III EWS Database. Season 2004

Jaroszyński M., Skowron J., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.

Acta Astronomica

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2006

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Vol. 56, No. 4

307--332

EN

We present 19 binary lens candidates from OGLE-III Early Warning System database for the season of 2004. We have also found five events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses of this and our previous studies (10 caustic crossing events of OGLE-II seasons 1997-1999 and 15 binary lens events of OGLE-III seasons 2002-2003) we find one case of extreme mass ratio binary (q≈0.005, a known planetary lens OGLE 2003-BLG-235/MOA 2003-BLG-53) and almost all other models with mass ratios in the range 0.1

19

The Optical Gravitational Lensing Experiment. Miras and Semiregular Variables in the Large Magellanic Cloud

Soszyński I., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Żebruń K., Szewczyk O., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2005

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Vol. 55, No. 4

331--348

EN

We use the OGLE-II and OGLE-III data in conjunction with the 2MASS near-infrared (NIR) photometry to identify and study Miras and Semiregular Variables (SRVs) in the Large Magellanic Cloud. We found in total 3221 variables of both types, populating two of the series of NIR period-luminosity (PL) sequences. The majority of these objects are double periodic pulsators, with periods belonging to both PL ridges. We indicate that in the period - Wesenheit index plane the oxygen-rich and carbon-rich AGB stars from the NIR PL sequences C, C' and D split into well separated ridges. Thus, we discover an effective method of distinguishing between O-rich and C-rich Miras, SRVs and stars with Long Secondary Periods using their V and I-band photometry. We present an empirical method of estimating the mean Ks magnitudes of the Long Period Variables using single-epoch Ks measurements and complete light curves in the I-band. We utilize these corrected magnitudes to show that the O-rich and C-rich Miras and SRVs follow somewhat different Ks-band PL relations.

20

Mass Estimates for Some of the Binary Lenses in OGLE-III Database

Jaroszyński M., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.

Acta Astronomica

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2005

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Vol. 55, No. 2

159--175

EN

We model binary microlensing events OGLE 2003-BLG-170, 267, and 291. Source angular sizes are measured for the events 267 and 291. Model fits to the light curves give parallaxes for the events 267 and 291, and relative source sizes for 170 and 267. Selfconsistency arguments provide extra limits on the models of the event 291. As a result we obtain likelihood estimate of the lens mass for the event 170, mass measurement based on angular size and parallax for 267, and narrow limits on mass in the case of 291. Brown dwarfs are most likely candidates for some of the lens components. The influence of the binary lens rotation and the Earth parallax may be important but hard to distinguish when modeling relatively short lasting binary lens events.