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1

The Optical Gravitational Lensing Experiment. Difference Image Analysis of LMC and SMC Data. The Method

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Żebruń K. , Soszyński I. , Woźniak P. R.

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tom Vol. 51, No. 4

303--316

EN

We describe the Difference Image Analysis (DIA) algorithms and software used to analyze four years (1997-2000) of OGLE-II photometric monitoring of the Magellanic Clouds, the calibration, the photometric error analysis and the search for variable stars. A preliminary analysis of photometric errors is based on the field LMC_SC2. A full catalog of more than 68 000 variable stars is presented in a separate publication.

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Binary Lenses in OGLE III EWS Database. Season 2005

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

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tom 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

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

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

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tom 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.

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The Optical Gravitational Lensing Experiment. Planetary and Low-Luminosity Object Transits in the Carina Fields of the Galactic Disk

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

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tom Vol. 52, No. 4

317--359

EN

We present results of the second "planetary and low-luminosity object transit" campaign conducted by the OGLE-III survey. Three fields (35'×35' each) located in the Carina regions of the Galactic disk (l≈290°) were monitored continuously in February-May 2002. About 1150 epochs were collected for each field. The search for low depth transits was conducted on about 103 000 stars with photometry better than 15 mmag. In total, we discovered 62 objects with shallow depth (≤0.08 mag) flat-bottomed transits. For each of these objects several individual transits were detected and photometric elements were determined. Also lower limits on radii of the primary and companion were calculated. The 2002 OGLE sample of stars with transiting companions contains considerably more objects that may be Jupiter-sized (R<1.6 RJup) compared to our 2001 sample. There is a group of planetary candidates with the orbital periods close to or shorter than one day. If confirmed as planets, they would be the shortest period extrasolar planetary systems. In general, the transiting objects may be extrasolar planets, brown dwarfs, or M-type dwarfs. One should be, however, aware that in some cases unresolved blends of regular eclipsing stars can mimic transits. Future spectral analysis and eventual determination of the amplitude of radial velocity should allow final classification. High resolution spectroscopic follow-up observations are, therefore, strongly encouraged. All photometric data are available to the astronomical community from the OGLE Internet archive.

5

Over 78 000 RR Lyrae Stars in the Galactic Bulge and Disk from the OGLE Survey

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Soszyński I. , Udalski A. , Wrona M. , Szymański M. K. , Pietrukowicz P. , Skowron J. , Skowron D. , Poleski R. , Kozłowski S. , Mróz P. , Ulaczyk K. , Rybicki K. , Iwanek P. , Gromadzki M.

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2019

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tom Vol. 69, No. 4

321--337

EN

We present an upgrade of the OGLE Collection of RR Lyrae stars in the Galactic bulge and disk. The size of our sample has been doubled and reached 78 350 RR Lyr variables, of which 56 508 are fundamental-mode pulsators (RRab stars), 21 321 pulsate solely in the first-overtone (RRc stars), 458 are classical double-mode pulsators (RRd stars), and 63 are anomalous RRd variables (including six triple-mode pulsators). For all the newly identified RR Lyr stars, we publish time-series photometry obtained during the OGLE Galaxy Variability Survey. We present the spatial distribution of RR Lyr stars on the sky, provide a list of globular clusters hosting RR Lyr variables, and discuss the Petersen diagram for multimode pulsators. We find new RRd stars belonging to a compact group in the Petersen diagram (with period ratios P 1O/PF≈0.74 and fundamental-mode periods P F≈0.44$ d) and we show that their spatial distribution is roughly spherically symmetrical around the Milky Way center.

6

The OGLE Collection of Variable Stars. Over 15 000 δ Scuti Stars in the Large Magellanic Cloud

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Soszyński I. , Pietrukowicz P. , Udalski A. , Skowron J. , Szymański M. K. , Poleski R. , Skowron D. M. , Kozłowski S. , Mróz P. , Iwanek P. , Wrona M. , Ulaczyk K. , Rybicki K. , Gromadzki M. , Mróz M.

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tom Vol. 73, No. 2

105--126

EN

We present the OGLE collection of δ Scuti stars in the Large Magellanic Cloud and in its foreground. Our dataset encompasses a total of 15 256 objects, constituting the largest sample of extragalactic δ Sct stars published so far. In the case of 12 δ Sct pulsators, we detected additional eclipsing or ellipsoidal variations in their light curves. These are the first known candidates for binary systems containing δ Sct components beyond the Milky Way. We provide observational parameters for all variables, including pulsation periods, mean magnitudes, amplitudes, and Fourier coefficients, as well as long-term light curves in the I- and V-bands collected during the fourth phase of the OGLE project. We construct the period-luminosity (PL) diagram, in which fundamental-mode and first-overtone δ Sct stars form two nearly parallel ridges. The latter ridge is an extension of the PL relation obeyed by first-overtone classical Cepheids. The slopes of the PL relations for δ Sct variables are steeper than those for classical Cepheids, indicating that the continuous PL relation for first-overtone δ Sct variables and Cepheids is non-linear, exhibiting a break at a period of approximately 0.5 d. We also report the enhancement of the OGLE collection of Cepheids and RR Lyr stars with newly identified and reclassified objects, including pulsators contained in the recently published Gaia DR3 catalog of variable stars. As a by-product, we estimate the contamination rate in the Gaia DR3 catalogs of Cepheids and RR Lyr variables.

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OGLE Collection of Star Clusters. New Objects in the Outskirts of the Large Magellanic Cloud

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Sitek M. , Szymański M. K. , Skowron D. M. , Udalski A. , Kostrzewa-Rutkowska Z. , Skowron J. , Karczmarek P. , Cieślar M. , Wyrzykowski Ł. , Kozłowski S. , Pietrukowicz P. , Soszyński I. , Mróz P. , Pawlak M. , Poleski R. , Ulaczyk K.

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tom Vol. 66, No. 3

255--267

EN

The Magellanic System (MS), consisting of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Magellanic Bridge (MBR), contains diverse sample of star clusters. Their spatial distribution, ages and chemical abundances may provide important information about the history of formation of the whole System. We use deep photometric maps derived from the images collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) to construct the most complete catalog of star clusters in the Large Magellanic Cloud using the homogeneous photometric data. In this paper we present the collection of star clusters found in the area of about 225 square degrees in the outer regions of the LMC. Our sample contains 679 visually identified star cluster candidates, 226 of which were not listed in any of the previously published catalogs. The new clusters are mainly young small open clusters or clusters similar to associations.

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Additional Galactic Cepheids from the OGLE Survey

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Soszyński I. , Udalski A. , Szymański M. K. , Pietrukowicz P. , Skowron J. , Skowron D. M. , Poleski R. , Kozłowski S. , Mróz P. , Ulaczyk K. , Rybicki K. , Iwanek P. , Wrona M. , Gromadzki M.

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tom Vol. 70, No. 2

101--119

EN

We report on the results of a comprehensive search for Cepheid variable stars in the fields photometrically monitored by the OGLE Galaxy Variability Survey. We identify 742 Cepheids not included in the first release of the OGLE Collection of Galactic Cepheids and reclassify several dozen previously published variables. The upgraded collection comprises 1974 classical, 1625 type II, and 119 anomalous Cepheids located in the area of about 3000 square degrees covering the disk and bulge of the Milky Way. We present the most interesting objects in our sample: an isolated group of long-period double-mode classical Cepheids pulsating in the fundamental mode and first overtone, the first known Galactic double-mode Cepheid with the second and third overtone excited, double-mode type II Cepheids, candidates for single-mode first-overtone BL Her stars, and Cepheids showing simultaneous eclipsing variability. We also discuss type II and anomalous Cepheids that are potential members of globular clusters.

9

The OGLE Collection of Variable Stars. Type II Cepheids in the Magellanic System

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Soszyński I. , Udalski A. , Szymański M. K. , Wyrzykowski Ł. , Ulaczyk K. , Poleski R. , Pietrukowicz P. , Kozłowski S. , Skowron D. , Skowron J. , Mróz P. , Rybicki K. , Iwanek P.

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tom Vol. 68, No. 2

89--109

EN

We present a nearly complete collection of type II Cepheids in the Magellanic System. The sample consists of 338 objects: 285 and 53 variables in the Large and Small Magellanic Clouds, respectively. Based on the pulsation periods and light-curve morphology, we classified 118 of our type II Cepheids as BL Her, 120 as W Vir, 34 as peculiar W Vir, and 66 as RV Tau stars. For all objects, we publish time-series {\it VI} photometry obtained during the OGLE-IV survey, from 2010 to the end of 2017. We present the most interesting individual objects in our collection: 16 type II Cepheids showing additional eclipsing or ellipsoidal variability, two RV Tau variables more than 2.5 mag fainter than other stars of this type in the LMC, an RVb star that drastically decreased the amplitude of the long-period modulation, type II Cepheids exhibiting significant amplitude and period changes, and an RV Tau star which undergoes interchanges of deep and shallow minima. We show that peculiar W Vir stars have markedly different spatial distribution than other subclasses of type II Cepheids, which indicates different evolutionary histories of these objects.

10

OGLE-ing the Magellanic System: Three-Dimensional Structure of the Clouds and the Bridge using RR Lyrae Stars

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Jacyszyn-Dobrzeniecka A. M. , Skowron D. M. , Mróz P. , Soszyński I. , Udalski A. , Pietrukowicz P. , Skowron J. , Poleski R. , Kozłowski S. , Wyrzykowski Ł. , Pawlak M. , Szymański M. K. , Ulaczyk K.

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tom Vol. 67, No. 1

1--35

EN

We present a three-dimensional analysis of a sample of 22 859 type ab RR Lyr stars in the Magellanic System from the OGLE-IV Collection of RR Lyr stars. The distance to each object was calculated based on its photometric metallicity and a theoretical relation between color, absolute magnitude and metallicity. The LMC RR Lyr distribution is very regular and does not show any substructures. We demonstrate that the bar found in previous studies may be an overdensity caused by blending and crowding effects. The halo is asymmetrical with a higher stellar density in its north-eastern area, which is also located closer to us. Triaxial ellipsoids were fitted to surfaces of a constant number density. Ellipsoids farther from the LMC center are less elongated and slightly rotated toward the SMC. The inclination and position angle change significantly with the $a$ axis size. The median axis ratio is 1:1.23:1.45. The RR Lyr distribution in the SMC has a very regular, ellipsoidal shape and does not show any substructures or asymmetries. All triaxial ellipsoids fitted to surfaces of a constant number density have virtually the same shape (axis ratio) and are elongated along the line-of-sight. The median axis ratio is 1:1.10:2.13. The inclination angle is very small and thus the position angle is not well defined. We present the distribution of RR Lyr stars in the Magellanic Bridge area, showing that the Magellanic Clouds' halos overlap. A comparison of the distributions of RR Lyr stars and Classical Cepheids shows that the former are significantly more spread and distributed regularly, while the latter are very clumped and form several distinct substructures.

11

The OGLE Collection of Variable Stars. Classical, Type II, and Anomalous Cepheids toward the Galactic Center

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Soszyński I. , Udalski A. , Szymański M. K. , Wyrzykowski Ł. , Ulaczyk K. , Poleski R. , Pietrukowicz P. , Kozłowski S. , Skowron D. M. , Skowron J. , Mróz P. , Pawlak M. , Rybicki K. , Jacyszyn-Dobrzeniecka A.

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tom Vol. 67, No. 4

297--316

EN

We present a collection of classical, typeII, and anomalous Cepheids detected in the OGLE fields toward the Galactic center. The sample contains 87 classical Cepheids pulsating in one, two or three radial modes, 924 type II Cepheids divided into BL Her, W Vir, peculiar W Vir, and RV Tau stars, and 20 anomalous Cepheids - first such objects found in the Galactic bulge. Additionally, we upgrade the OGLE Collection of RR Lyr stars in the Galactic bulge by adding 828 newly identified variables. For all Cepheids and RRLyr stars, we publish time-series VI photometry obtained during the OGLE-IV project, from 2010 through 2017. We discuss basic properties of our classical pulsators: their spatial distribution, light curve morphology, period-luminosity relations, and position in the Petersen diagram. We present the most interesting individual objects in our collection: a typeII Cepheid with additional eclipsing modulation, WVir stars with the period doubling effect and the RVb phenomenon, a mode-switching RR Lyr star, and a triple-mode anomalous RRd star.

12

Final Release of the OGLE Collection of Cepheids and RR Lyrae Stars in the Magellanic System. The Outer Regions

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Soszyński I. , Udalski A. , Szymański M. K. , Pietrukowicz P. , Skowron J. , Skowron D. M. , Poleski R. , Kozłowski S. , Mróz P. , Ulaczyk K. , Rybicki K. , Iwanek P. , Wrona M.

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tom Vol. 69, No. 2

87--99

EN

We present the final release of the OGLE collection of classical pulsators (Cepheids and RR Lyr stars) in the Large and Small Magellanic Clouds. The sky coverage has been increased from 670 to 765 square degrees compared to the previous edition of our collection. We also add some Cepheids and RR Lyr stars found by the Gaia team and reclassify three Cepheids. Ultimately, our collection consists of 9650 classical Cepheids, 343 type II Cepheids, 278 anomalous Cepheids, and 47 828 RR Lyr stars inside and toward the Magellanic System.

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The OGLE Collection of Variable Stars: Over 18 000 Rotating Variables toward the Galactic Bulge

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Iwanek P. , Soszyński I. , Stępień K. , Kozłowski S. , Skowron J. , Udalski A. , Szymański M. K. , Wrona M. , Pietrukowicz P. , Poleski R. , Mróz P. , Ulaczyk K. , Skowron D. M. , Gromadzki M. , Rybicki K. , Mróz M. J. , Ratajczak M.

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tom Vol. 74, No. 1

1--25

EN

Stellar rotation, a key factor influencing stellar structure and evolution, also drives magnetic activity, which is manifested as spots or flares on stellar surface. Here, we present a collection of 18 443 rotating variables located toward the Galactic bulge, identified in the photometric database of the Optical Gravitational Lensing Experiment (OGLE) project. These stars exhibit distinct magnetic activity, including starspots and flares. With this collection, we provide long-term, time-series photometry in Cousins I- and Johnson V-band obtained by OGLE since 1997, and basic observational parameters, i.e., equatorial coordinates, rotation periods, mean brightness, and brightness amplitudes in both bands. This is a unique dataset for studying stellar magnetic activity, including activity cycles.