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One Thousand New Dwarf Novae from the OGLE Survey

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

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2015

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tom Vol. 65, No. 4

313--328

EN

We present one of the largest collections of dwarf novae (DNe) containing 1091 objects that have been discovered in the long-term photometric data from the Optical Gravitational Lensing Experiment (OGLE) survey. They were found in the OGLE fields toward the Galactic bulge and the Magellanic Clouds. We analyze basic photometric properties of all systems and tentatively find a population of DNe from the Galactic bulge. We identify several dozen of WZ Sge-type DN candidates, including two with superhump periods longer than 0.09 d. Other interesting objects include SU UMa-type stars with "early" precursor outbursts or a Z Cam-type star showing outbursts during standstills. We also provide a list of DNe which will be observed during the K2 Campaign 9 microlensing experiment in 2016. Finally, we present the new OGLE-IV real-time data analysis system: CVOM, which has been designed to provide continuous real time photometric monitoring of selected CVs.

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Superhumps and their Evolution during Superoutbursts

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Smak J.

Acta Astronomica

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2016

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tom Vol. 66, No. 1

75--83

EN

Light curves of superhumps and their evolution during superoutbursts are analyzed by decomposing them into their Fourier components, including the fundamental mode and the first three overtones. The amplitudes of the fundamental mode are found to decrease significantly during superoutburst while those of the overtones remain practically constant. The phases of maxima of the fundamental mode increase systematically during superoutburst while those of the overtones - systematically decrease. The combination of the two effects is responsible for the characteristic evolution of superhump light curves: the appearance and growth of the secondary humps and the spurious phase jumps in the (O-C) diagrams. Two intrepretations are possible. Either that instead of just one superhump period Psh there are four periods Pk which resemble - but are significantly different from - the fundamental mode and the first three overtones of Psh. Or - more likely - that those time-dependent phase shifts are genuine.

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The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55

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Kaluzny J. , Thompson I. B. , Krzeminski W. , Zloczewski K.

Acta Astronomica

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2010

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tom 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.

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On the Periods and Nature of Superhumps

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Smak J.

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2020

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tom Vol. 70, No. 4

317--321

EN

It is commonly accepted that the periods of superhumps can be satisfactorily explained within a model involving apsidal motion of the accretion disk provided the frequency of the apsidal motion in addition to the dynamical term includes also the pressure effects. Using a larger sample of systems with reliable mass ratios it is shown, however, that this view is not true and the model requires further modifications.

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Direct Evidence for Modulated Irradiation of Secondary Components in Dwarf Novae during Superoutbursts

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Smak J.

Acta Astronomica

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2011

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tom Vol. 61, No. 1

59--69

EN

Contribution from the irradiated secondary component is detected in the light curves of five dwarf novae observed during superoutbursts. Their superhump light curves show that irradiation is modulated with the superhump phase. This strengthens the new interpretation of superhumps as being due to the irradiation controlled mass transfer rate resulting in modulated dissipation of the kinetic energy of the stream.

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

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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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tom 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.

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On the Enhanced Mass Outflow during Dwarf Nova Outbursts

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Smak J.

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tom Vol. 54, No. 4

429--432

EN

During dwarf nova outbursts the secondary component is irradiated by the boundary layer and the white dwarf. The problem is whether the hotter material from irradiated regions can reach the vicinity of the inner Lagrangian point L1, producing an enhanced mass outflow. Osaki and Meyer (2003, 2004) presented a model in which the pressure gradient in the direction towards L1 is always exactly balanced by the Coriolis force and, consequently, does not produce any acceleration and motion in that direction. Instead the material is predicted to flow in the perpendicular direction along the shadow boundary. It is shown that this model, as based on an arbitrary assumption, is incorrect. My model (Smak 2004) produced flow trajectories directed (due to the pressure gradient) toward the equator, but deflected (due to the Coriolis force) with respect to the direction toward L1. In systems with short orbital periods the effects of the Coriolis force were not large enough, however, to prevent the material from reaching L1. Criticism of this model by Osaki and Meyer (2004), concerning incomplete treatment of the equation of continuity, is shown to result primarily from misunderstandings.

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On the Periods of Negative Superhumps and the Nature of Superhumps

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Smak J.

Acta Astronomica

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2013

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tom Vol. 63, No. 1

109--114

EN

Osaki and Kato interpreted variations of the negative superhump periods, discovered by them in dwarf nova V1504 Cyg, as evidence in favor of the thermal-tidal instability model for superoutbursts. It is shown that their interpretation was incorrect. The observational evidence is recalled showing that superoutbursts are due to the enhanced mass transfer rate.

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On the Mass Transfer Rate in SS Cyg

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Smak J.

Acta Astronomica

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2010

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tom Vol. 60, No. 1

83--89

EN

The mass transfer rate in SS Cyg at quiescence, estimated from the observed luminosity of the hot spot, is log Mtr=16.8±0.3. This is safely below the critical mass transfer rates of log Mcrit=18.1 (corresponding to log Tcrit0=3.88) or log Mcrit=17.2 (corresponding to the "revised" value of log Tcrit0=3.65). The mass transfer rate during outbursts is strongly enhanced.

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Enhanced Mass Transfer in U Geminorum during its Outbursts and Superoutburst

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Smak J.

Acta Astronomica

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2005

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tom Vol. 55, No. 3

315--320

EN

The mass transfer rate in U Gem at quiescence, estimated to be M≈1.3-2.0×1016 g/s, is used to calculate the amount of mass ΔMtr transfered to the disk during quiescence. Light curves of U Gem are used to estimate the amounts of mass ΔMaccr accreted during its three types of outbursts. In the case of wide outbursts and the 1985 superoutburst ΔMaccr are much larger than ΔMtr, indicating significant enhancement in the mass transfer by a factor of f≈20-50. There is no evidence for comparable enhancement during narrow outbursts.

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2009 Superoutburst of Dwarf Nova 1RXS J053234.9+624755

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Rutkowski A. , Olech A. , Poleski R. , Sobolewska M. , Kankiewicz P. , Ak T. , Boyd D.

Acta Astronomica

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2010

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tom Vol. 60, No. 4

337--355

EN

We present photometric observations of the dwarf nova 1RXS J053234.9+624755. We performed a detailed analysis of the superoutburst that occurred in August 2009. We found the superhump period to be Psh=0.057122(14) days. Based on the O-C diagram we conclude that Psh increased during the plateau at the rate of dPsh/dt=(9.24±1.4)×10-5. Both the O-C analysis and evolution of the superhumps light curve favor the model in which superhumps originate in a variable source located in the vicinity of the hot spot. In addition, the evolution of the light curve suggests that the superhump light source approaches the disk plane as the superoutburst declines. Detailed analysis of the superoutburst plateau phase enabled us to detect a signal which we interpret as apsidal motion of the accretion disk. We detected additional modulations during the final stage of the superoutburst characterized by periods of 104 s and 188 s which we tentatively interpret as quasi periodic oscillations. Estimations of A0 and An are in agreement with the dependence between the amplitude of superhumps and the orbital inclination.