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1

AM CVn - System Parameters and Gravitational Waves

Smak J.

Acta Astronomica

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2023

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Vol. 73, No. 3

227--232

EN

System parameters of AM CVn are re-determined: M1=0.86±0.18 M☉, M2=0.103±0.0022 M☉, A=1.508±0.100×1010 cm, and i=69±3°. The secondary component of the system is a semi-degenerate helium star loosing mass at a rate M=4.93±1.65×10-9 M☉/yr. The accretion disk is sufficiently hot to avoid thermal instability. The orbital light curve recovered from observations made in 1962 shows minimum shifted to phase φ=0.50, corresponding to O-C=0.0060 d. Together with mimima observed in the years 1992-1999 this implies that the orbital period is increasing at a rate of dP/dt≈8.5×10-13 - consistent with predictions involving the emission of gravitational waves.

2

On the Critical Mass Ratio for the 3:1 Resonance in Accretion Disks

Smak J.

Acta Astronomica

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2020

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Vol. 70, No. 4

313--315

EN

The 3:1 resonance between the orbital frequency of the binary system and the orbital frequency of the outer parts of the disk can occur only in systems with mass ratio smaller than certain critical value. It is shown that qcrit=0.22, i.e. smaller than obtained earlier by other authors (qcrit=0.25-0.39). This implies that the tidal-resonance model fails to explain superhumps in systems with orbital periods above the period gap.

3

RW Tri - its Negative Superhumps and System Parameters

Smak J.

Acta Astronomica

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2019

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Vol. 69, No. 1

79--85

EN

Negative superhumps are detected in the light curves of RW Tri observed in September 1994 and November/December 1957. New system parameters, obtained using K2 and V2,rotsin i and q (estimated from PnSH), are M1=0.60±0.20 M☉, M2=0.48±0.15 M☉, A=1.13±0.09×1011 cm and i=72°.5±2°.5.

4

V2676 Oph: Estimating Physical Parameters of a Moderately Fast Nova

Raj A., Pavana M., Kamath U. S., Anupama G. C., Walter M. F.

Acta Astronomica

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2018

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Vol. 68, No. 1

79--88

EN

Using our previously reported observations, we derive some physical parameters of the moderately fast nova V2676 Oph 2012 #1. The best-fit Cloudy model of the nebular spectrum obtained on 2015 May 8 shows a hot white dwarf source with TBB≈1.0×105 K having a luminosity of 1.0×1038 erg/s. Our abundance analysis shows that the ejecta are significantly enhanced relative to solar, He/H=2.14, O/H=2.37, S/H=6.62 and Ar/H=3.25. The ejecta mass is estimated to be 1.42×10-5 M⊙. The nova showed a pronounced dust formation phase after 90 d from discovery. The J-H and H-K colors were very large as compared to other molecule- and dust-forming novae in recent years. The dust temperature and mass at two epochs have been estimated from spectral energy distribution fits to infrared photometry.

5

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.

6

On the Light Curves of AM CVn

Smak J.

Acta Astronomica

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2017

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Vol. 67, No. 1

63--69

EN

Light curves of AM CVn are analyzed by decomposing them into their Fourier components. The amplitudes of the fundamental mode and overtones of the three components: the superhumps, the negative superhumps and the orbital variations, are found to be variable. This implies that variations in the shape of the observed light curve of AM CVn are not only due to the interference between those components, but also due to the intrinsic variability within these components.

7

DW UMa and the Irradiation Modulated Mass Transfer Model for Superhumps

Smak J.

Acta Astronomica

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2017

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Vol. 67, No. 3

273--280

EN

The light curves of the permanent superhumper DW UMa are analyzed in order to determine the amplitudes of its superhumps, A SH, and the amplitudes of the periodic light variations with the beat period - the irradiation amplitudes - Airr. The resulting values of ASH and Airr, together with other values from the literature, turn out to be correlated thereby confirming the irradiation modulated mass transfer model for superhumps.

8

Superhumps and their Evolution during Superoutbursts

Smak J.

Acta Astronomica

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2016

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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.

9

Ultra-Short-Period Binary Systems in the OGLE Fields Toward the Galactic Bulge

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

Acta Astronomica

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2015

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Vol. 65, No. 1

39--62

EN

We present a sample of 242 ultra-short-period (Porb <0.22 d) eclipsing and ellipsoidal binary stars identified in the OGLE fields toward the Galactic bulge. Based on the light curve morphology, we divide the sample into candidates for contact binaries and non-contact binaries. In the latter group we distinguish binary systems consisting of a cool main-sequence star and a B-type subdwarf (HW Vir stars) and candidates for cataclysmic variables, including five eclipsing dwarf novae. One of the detected eclipsing binary systems - OGLE-BLG-ECL-000066 - with the orbital period below 0.1 d, likely consists of M dwarfs in a nearly contact configuration. If confirmed, this would be the shortest-period M-dwarf binary system currently known. We discuss possible evolutionary mechanisms that could lead to the orbital period below 0.1 d in an M-dwarf binary.

10

One Thousand New Dwarf Novae from the OGLE Survey

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

Acta Astronomica

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2015

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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.

11

Hot Spot in Eclipsing Dwarf Nova IY Ursae Majoris during Quiescence and Normal Outburst

Bąkowska K., Olech A.

Acta Astronomica

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2015

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Vol. 65, No. 4

351--360

EN

We present the analysis of hot spot brightness in light curves of the eclipsing dwarf nova IY UMa during its normal outburst in March 2013 and in quiescence in April 2012 and in October 2015. Examination of four reconstructed light curves of the hot spot eclipses showed directly that the brightness of the hot spot changed significantly only during the outburst. The brightness of the hot spot, before and after the outburst, was on the same level. Thus, based on the behavior of the hot spot, IY UMa during its normal outburst follows the disk-instability model.

12

TT Ari and its Quasi-Periodic Oscillations

Smak J.

Acta Astronomica

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2014

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Vol. 64, No. 2

167--175

EN

Quasi-periodic oscillation (QPO) of TT Ari are transient, short-lived phenomena. They appear and disappear and their periods and amplitudes vary on a time scale as short as 1 hour. Consequently the periodograms covering longer intervals of time are generally meaningless.

13

OGLE-IV Real-Time Transient Search

Wyrzykowski Ł., Kostrzewa-Rutkowska Z., Kozłowski S., Udalski A., Poleski R., Skowron J., Blagorodnova N., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Ulaczyk K., Pietrukowicz P., Mróz Michał

Acta Astronomica

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2014

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Vol. 64, No. 3

197--232

EN

We present the design and first results of a real-time search for transients within the 650 sq. deg. area around the Magellanic Clouds, conducted as part of the OGLE-IV project and aimed at detecting supernovae, novae and other events. The average sampling of about four days from September to May, yielded a detection of 238 transients in 2012/2013 and 2013/2014 seasons. The superb photometric and astrometric quality of the OGLE data allows for numerous applications of the discovered transients. We use this sample to prepare and train a Machine Learning-based automated classifier for early light curves, which distinguishes major classes of transients with more than 80% of correct answers. Spectroscopically classified 49 supernovae Type Ia are used to construct a Hubble Diagram with statistical scatter of about 0.3 mag and fill the least populated region of the redshifts range in the Union sample. We investigate the influence of host galaxy environments on supernovae statistics and find the mean host extinction of AI=0.19±0.10 mag and AV=0.39±0.21 mag based on a subsample of supernovae Type Ia. We show that the positional accuracy of the survey is of the order of 0.5 pixels (0.13'') and that the OGLE-IV Transient Detection System is capable of detecting transients within the nuclei of galaxies. We present a few interesting cases of nuclear transients of unknown type. All data on the OGLE transients are made publicly available to the astronomical community via the OGLE website.

14

Hot Spot Manifestation in Eclipsing Dwarf Nova HT Cassiopeiae

Bąkowska K., Olech A.

Acta Astronomica

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2014

|

Vol. 64, No. 3

247--259

EN

We report the detection of a hot spot in the light curves of the eclipsing dwarf nova HT Cas during its superoutburst in 2010 November. Analysis of the eight reconstructed light curves of the hot spot eclipses showed directly that the brightness of the hot spot was changing significantly during the superoutburst. Thereby, detected hot spot manifestation in HT Cas is the newest observational evidence for the EMT model for dwarf novae.

15

CzeV404 - an Eclipsing Dwarf Nova in the Period Gap During its July 2014 Superoutburst

Bąkowska K., Olech A., Pospieszyński R., Martinelli F., Marciniak A.

Acta Astronomica

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2014

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Vol. 64, No. 4

337--348

EN

Results of the CCD observations of CzeV404 are presented. During the season of June-August 2014 we detected one outburst and one superoutburst of the star. Clear superhumps with the period of Psh=0.10472(2) days were observed. The superhump period was decreasing with a high value of dP/dt=-2.43(8)×10-4. From 17 eclipses we calculated the orbital period with the value of Porb=0.0980203(6) days which confirms that CzeV404 belongs to period gap objects and it is the longest orbital period of an eclipsing SU UMa star. Based on superhump and orbital period determinations, the period excess ε=6.8%±0.02% and the mass ratio q≈0.32; of the system were obtained.

16

On the Periods of Negative Superhumps and the Nature of Superhumps

Smak J.

Acta Astronomica

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2013

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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.

17

On the Nature of Superhumps

Smak J.

Acta Astronomica

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2013

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Vol. 63, No. 3

369--377

EN

Further evidence is presented supporting the alternative interpretation of superhumps as being due to irradiation modulated periodically variable mass transfer rate. NZ Boo, HT Cas and PU UMa are added to the sample of high inclination dwarf novae showing - during their superoutbursts - modulation of the observed brightness of the disk with beat period. Simple model calculations confirm earlier hypothesis that this modulation is due to a non-axisymmetric structure of the outer parts of the disk, involving the azimuthal dependence of their geometrical thickness, rotating with the beat period. The modulation amplitude Amod is found to decrease during superoutbursts. In particular, it is found that during two superoutbursts of OY Car the rate of decline of the superhump amplitude dASH/dt was correlated with the rate of decline dAmod/dt. This leads to a simple explanation for the decreasing amplitudes of superhumps: it is a consequence of the decreasing modulation amplitude.

18

On the Eclipsing Cataclysmic Variable Star HBHA 4705-03

Rutkowski A., Ak T., Marsh T. R., Eker Z.

Acta Astronomica

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2013

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Vol. 63, No. 2

225--238

EN

We present observations and analysis of a new eclipsing binary HBHA 4705-03. Using decomposition of the light curve into accretion disk and hot spot components, we estimated photometrically the mass ratio of the studied system to be q=0.62±0.07. Modeling of the system yields the following fundamental parameters: white dwarf mass M1=(0.8±0.2) Msun, secondary mass M2=(0.497±0.05) Msun, orbital radius a=1.418 Rsun, orbital inclination i=(81.°58±0.°5), accretion disk radius rd/a=0.366±0.002, and accretion rate M=(2.5±2)x1018 [g/s] (3×10-8 Msun/yr). Power spectrum analysis revealed a set of possible low-period Quasi Periodic Oscillations centered at the frequencies f1=0.00076 Hz, f2=0.00048 Hz and f3=0.00036 Hz. The system B-V=0.04 mag corresponds to a dwarf nova color during an outburst. The light curves of HBHA 4705-03 suggest that it is a nova-like variable star.

19

Fifty Years of TT Arietis

Smak J.

Acta Astronomica

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2013

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Vol. 63, No. 4

453--463

EN

Results of photometric observations of the permanent negative superhumper TT Ari in 1961/62 and 1966 are presented. Together with data from the literature they are used to discuss the negative superhump amplitudes AnSH and the amplitudes Abeat of the modulation with the beat period Pbeat. Both amplitudes are shown to vary considerably from one season to another. Three correlations are found: (1) between AnSH and Abeat, (2) between AnSH and PnSH, and (3) between Abeat and Pbeat.

20

Dwarf Novae in the OGLE Data. II. Forty New Dwarf Novae in the OGLE-III Galactic Disk Fields

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

Acta Astronomica

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2013

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Vol. 63, No. 2

135--158

EN

We report the discovery of forty erupting cataclysmic variable stars in the OGLE-III Galactic disk fields: seventeen objects of U Gem type, four of Z Cam type, and nineteen stars showing outbursts and superoutbursts typical for SU UMa type dwarf novae. In the case of five stars we were able to estimate their supercycle lengths. The obtained lengths are in the range of 20-90 d, generally between the typical SU UMa type variables and a few objects classified as the ER UMa type variables. Since there is no significant difference between the two types but a higher mass-transfer rate resulting in more frequent outbursts and superoutbursts in the ER UMa type stars, we propose to discard this type as a separate class of variables. We note that in one of the SU UMa type stars, OGLE-GD-DN-039, we found a negative supercycle period change, in contrast to other active systems of this type. Two of the new OGLE objects showed long-duration WZ Sge-like superoutbursts followed by a sequence of echo outbursts. All stars reported in this paper are part of the OGLE-III Catalog of Variable Stars.