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The OGLE Collection of Variable Stars. Over 45 000 RR~Lyrae Stars in the Magellanic System

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.

Acta Astronomica

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2016

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Vol. 66, No. 2

131--147

EN

We present the largest collection of RR Lyrae stars in the Magellanic System and in its foreground. The sample consists of 45 451 RR Lyr stars, of which 39 082 were detected toward the Large Magellanic Cloud and 6369 toward the Small Magellanic Cloud. We provide long-term time-series photometric measurements collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV). We discuss several potential astrophysical applications of our collection: investigation of the structure of the Magellanic Clouds and the Galactic halo, studies of the globular clusters in the Magellanic System, analysis of double-mode RR Lyr stars, and search for RR Lyr stars in eclipsing binary systems.

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Wide-Field Variability Survey of the Globular Cluster M 79 and a New Period-Luminosity Relation for SX Phe Stars

Kopacki G.

Acta Astronomica

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2015

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Vol. 65, No. 1

81--106

EN

We present the results of a search for variable stars in a 26×39 arcmin² field around globular cluster M 79 (NGC 1904). The search was made by means of an extended version of image subtraction, which allows us to analyze in a uniform manner CCD frames obtained with different telescopes and cameras of different sizes and resolutions. The search resulted in finding 20 new variable stars, among which 13 are cluster members. The members include one new RR Lyr star of subtype c, three SX Phe stars, and nine variable red giants. We also show that V7 is a W Vir star with a period of 13.985 d. Revised mean periods of RRab and RRc stars, ⟨P⟩_ab=0.71 d and ⟨P⟩=0.34 d, respectively, and relative percentage of RRc stars, N_c/(N_ab+N_c)=45% confirm that M 79 belongs to the Oosterhoff II group of globular clusters. The mean V magnitude of the horizontal branch of M 79 based on ten RR Lyr stars has been estimated to be V=⟨V⟩_RR=16.11±0.03 mag. In one RRc star, V9, light changes with three close frequencies were detected, indicating excitation of nonradial modes. An SX Phe star, V18, is a double-mode pulsator with two radial modes excited, fundamental and first overtone. Moreover, we have discovered two SX Phe or δ Sct stars and one W UMa type system, all likely field objects. We also studied the period-luminosity relation for SX Phe stars. Using 62 fundamental and fundamentalized periods of radial double-mode and high-amplitude SX Phe stars known in Galactic globular clusters, we have derived the slope and zero point of this relation to be, -3.3±0.27 and 2.68±0.03 mag (at log(P/d)=-1.24), respectively.

3

The OGLE Collection of Variable Stars. Anomalous Cepheids in the Magellanic Clouds

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

Acta Astronomica

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2015

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Vol. 65, No. 3

233--250

EN

We present a collection of 250 anomalous Cepheids (ACs) discovered in the OGLE-IV fields toward the Large (LMC) and Small Magellanic Cloud (SMC). The LMC sample is an extension of the OGLE-III Catalog of ACs published in 2008, while the SMC sample contains the first known bona fide ACs in this galaxy. The total sample is composed of 141 ACs in the LMC and 109 ACs in the SMC. All these stars pulsate in single modes: fundamental (174 objects) or first overtone (76 objects). Additionally, we report the discovery of four ACs located in the foreground of the Magellanic Clouds. These are the first unambiguously identified fundamental-mode ACs known in the Galactic field. We demonstrate that the coefficients φ21 and φ31 determined by the Fourier light curve decomposition are useful discriminators between classical Cepheids and ACs, at least in the LMC and in the field of the Milky Way. In the SMC, the light curve shapes and mean magnitudes of short-period classical Cepheids make them similar to ACs, which is a source of difficulties in the discrimination of both classes of pulsators. The presence of unidentified ACs in the catalogs of classical Cepheids may be partly responsible for the observed non-linearity of the period--luminosity relation observed for short-period Cepheids in the SMC. We compare spatial distributions of ACs, classical Cepheids and RR Lyr stars. We show that the distribution of ACs resembles that of old stars (RR Lyr variables), although in the LMC there are visible structures typical for young population (classical Cepheids): the bar and spiral arms. This may suggest that ACs are a mixture of relatively young stars and mergers of very old stars.

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Over 38 000 RR Lyrae Stars in the OGLE Galactic Bulge Fields

Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Mróz P., Skowron J., Kozłowski S., Poleski R., Skowron D., Pietrzyński G., Wyrzykowski L., Ulaczyk K., Kubiak M.

Acta Astronomica

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2014

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Vol. 64, No. 3

177--196

EN

We present the most comprehensive picture ever obtained of the central parts of the Milky Way probed with RR Lyr variable stars. This is a collection of 38 257 RR Lyr stars detected over 182 square degrees monitored photometrically by the Optical Gravitational Lensing Experiment (OGLE) in the most central regions of the Galactic bulge. The sample consists of 16 804 variables found and published by the OGLE collaboration in 2011 and 21 453 RR Lyr stars newly detected in the photometric databases of the fourth phase of the OGLE survey (OGLE-IV). 93% of the OGLE-IV variables were previously unknown. The total sample consists of 27 258 RRab, 10 825 RRc, and 174 RRd stars. We provide OGLE-IV I- and V-band light curves of the variables along with their basic parameters. About 300 RR Lyr stars in our collection are plausible members of 15 globular clusters. Among others, we found the first pulsating variables that may belong to the globular cluster Terzan 1 and the first RRd star in the globular cluster M54. Our survey also covers the center and outskirts of the Sagittarius Dwarf Spheroidal Galaxy enabling studies of the spatial distribution of the old stellar population from this galaxy. A group of double-mode RR Lyr stars with period ratios around 0.740 forms a stream in the sky that may be a relic of a cluster or a dwarf galaxy tidally disrupted by the Milky Way. Three of our RR Lyr stars experienced a pulsation mode switching from double-mode to single fundamental mode or vice versa. We also present the first known RRd stars with large-amplitude Blazhko effect.

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The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. Type II Cepheids in the Galactic Bulge - Supplement

Soszyński I., Udalski A., Pietrukowicz P., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S.

Acta Astronomica

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2013

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Vol. 63, No. 1

37--40

EN

We report the discovery of additional 22 RV Tau stars located in the OGLE-II and OGLE-III fields toward the Galactic bulge, increasing to 357 objects the OGLE-III catalog of type II Cepheids in the Galactic center. Four of the newly detected RV Tau stars belong to the RVb class, i.e., they show large-amplitude, long-period modulation of the mean luminosity. In the updated catalog, the relative number of RV Tau stars in the whole sample of the Galactic bulge type II Cepheids is similar to the Magellanic Cloud samples.

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

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

Acta Astronomica

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2010

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Vol. 60, No. 2

91--107

EN

The eighth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains type II Cepheids in the Small Magellanic Cloud (SMC). The sample consists of 43 objects, including 17 BL Her, 17 W Vir and 9 RV Tau stars (first examples ever found in the SMC). Seven stars have been classified as peculiar W Vir stars - a recently identified subclass of type II Cepheids. These stars have distinctive light curves, are brighter and bluer than the ordinary W Vir variables. We confirm that a large fraction of the peculiar W Vir stars are members of binary systems. Three type II Cepheids exhibit eclipsing variations superimposed on the pulsation light curves, and three other objects show long-period ellipsoidal variability. All stars with the indication of binarity display secondary periods which may be interpreted as amplitude and/or phase modulations of the pulsation light curves with periods equal to the orbital periods or half the orbital periods. We do not have any model for these modulations, however this phenomenon rules out a possibility of the optical blends of a pulsating star and a binary system. For each object the multi-epoch V- and I-band photometry collected over 8 or 13 years of observations and finding charts are available to the astronomical community from the OGLE Internet archive.

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Fourier Analysis of Hipparcos Photometry of Cepheid Variables

Zakrzewski B., Ogłoza W., Moskalik P.

Acta Astronomica

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2000

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Vol. 50, No. 3

387--397

EN

Fourier parameters have been computed for 240 field Cepheids observed by the Hipparcos satellite. We have identified three new Population I overtone Cepheids: V411 Lac, V898 Cen and V572 Aql. We have compared Fourier progressions of Population I and Population II Cepheids. The possibility of using Fourier parameters to distinguish between the two types is discussed.