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1
Content available remote AM CVn - System Parameters and Gravitational Waves
Smak J.
Acta Astronomica
|
2023
|
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
Content available remote On the Orbital Period and Models of V Sge
Smak J.
Acta Astronomica
|
2022
|
Vol. 72, No. 1
21--29
EN
The orbital period of V Sge is decreasing at a rate which increased from dP/dt=-(4.11±0.33)×10-10 in 1962 to -(5.44±0.61)× 10-10 in 2022. This implies that the mass transfer from the secondary component is accelerating. From the evidence based on the orbital period variations, combined with estimates of the mass loss from the system based on radio observations, it follows that (1) the mass transfer rate from the secondary component is larger than M2=-5×10-6 M☉/yr, possibly as large as M2=-2.5×10-5 M☉/yr, and (2) the mass loss rate from the primary component is M1=-4×10-7 M☉/yr or larger. Close similarity of V Sge to binary Wolf-Rayet stars supports the model with primary component being a hot, evolved star loosing its mass. Several arguments are presented which exclude the alternative model with primary component being a white dwarf with an accretion disk.
3
Content available remote On the Periods and Nature of Superhumps
Smak J.
Acta Astronomica
|
2020
|
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.
4
Content available remote On the Critical Mass Ratio for the 3:1 Resonance in Accretion Disks
Smak J.
Acta Astronomica
|
2020
|
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.
5
Content available remote RW Tri - its Negative Superhumps and System Parameters
Smak J.
Acta Astronomica
|
2019
|
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.
6
Content available remote On the Light Curves of AM CVn
Smak J.
Acta Astronomica
|
2017
|
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
Content available remote DW UMa and the Irradiation Modulated Mass Transfer Model for Superhumps
Smak J.
Acta Astronomica
|
2017
|
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
Content available remote Superhumps and their Evolution during Superoutbursts
Smak J.
Acta Astronomica
|
2016
|
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
Content available remote TT Ari and its Quasi-Periodic Oscillations
Smak J.
Acta Astronomica
|
2014
|
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.
10
Content available remote On the Periods of Negative Superhumps and the Nature of Superhumps
Smak J.
Acta Astronomica
|
2013
|
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.
11
Content available remote On the Nature of Superhumps
Smak J.
Acta Astronomica
|
2013
|
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.
12
Content available remote Fifty Years of TT Arietis
Smak J.
Acta Astronomica
|
2013
|
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.
13
Content available remote Stream Overflow in Z Cha and OY Car during Quiescence
Smak J.
Acta Astronomica
|
2012
|
Vol. 62, No. 2
213--217
EN
Eclipses of the hot spot in Z Cha and OY Car observed by many authors during their quiescence are re-analyzed. Distances of the spot from the center of the disk rs are determined from phases of ingress and egress. In the case of several eclipses of Z Cha and nearly all eclipses of OY Car it is found that rs(egress)s(ingress). This is interpreted as being due to the effects of stream overflow and implies that those values of rs are not representative for the radius of the disk rd. The rs(ingress)-dt relations (where dt is the time since last outburst) are improved when points affected by the stream overflow are omitted.
14
Content available remote Direct Evidence for Modulated Irradiation of Secondary Components in Dwarf Novae during Superoutbursts
Smak J.
Acta Astronomica
|
2011
|
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.
15
Content available remote Superhumps and their Amplitudes
Smak J.
Acta Astronomica
|
2010
|
Vol. 60, No. 4
357--371
EN
Superhump amplitudes observed in dwarf novae during their superoutbursts depend on orbital inclination: the maximum amplitudes in systems with low inclinations are A0≈0.25 mag, while at higher inclinations they increase from A0≈0.3 mag to A0≈0.6 mag. The mean maximum superhump amplitudes normalized to the average luminosity of the disk are: n>=0.34±0.02 mag in low inclination systems and only n>=0.17±0.01 mag in high inclination systems. This shows that at high inclinations the superhump light source is partly obscured by the disk edge and implies that it is located close to the disk surface but extends sufficiently high above that surface to avoid full obscuration. Superhump amplitudes in high inclination systems show modulation with beat phase (φb), interpreted as being due to azimuth-dependent obscuration effects in a non-axisymmetric disk. In addition they show modulation with 2φb which implies that the orientation of the superhump light source is correlated with the direction of the stream. The dependence of superhump amplitudes on orbital inclination and their modulation with beat phase eliminate the tidal-resonance model for superhumps. Instead they support an alternative interpretation of superhumps as being due to periodically modulated dissipation of the kinetic energy of the stream. Superhump amplitudes in permanent superhumpers are =0.12 mag, i.e., much smaller than the maximum amplitudes observed during superoutbursts.
16
Content available remote On the Mass Transfer Rate in SS Cyg
Smak J.
Acta Astronomica
|
2010
|
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.
17
Content available remote Z Cha and its Superhumps
Smak J.
Acta Astronomica
|
2009
|
Vol. 59, No. 1
109--120
EN
The superhump eclipse light curves are re-determined for five eclipses of Z Cha (E54036, E54037, E67877, E74693, E74694) observed by Warner and O'Donoghue (1988) during its superoutbursts. Qualitatively they are similar to those obtained by O'Donoghue (1990), showing two local minima at φ≈-0.05 and 0.04. Arguments are then presented which imply that the first minimum is not due to an occultation but is produced by absorption effects in the overflowing parts of the stream. The location of the superhump light source (SLS) determined from the analysis of the second minimum coincides with the trajectory of the overflowing parts of the stream. The light curve of the sixth eclipse (E77878) could be simply decomposed into its disk and superhump components. The location of SLS, obtained from the analysis of the SLS eclipse light curve, coincides in this case with the position of the standard hot spot. This implies that superhumps are due to modulated mass transfer rate resulting in periodically enhanced dissipation of the kinetic energy of the stream.
18
Content available remote On the Origin of Tilted Disks and Negative Superhumps
Smak J.
Acta Astronomica
|
2009
|
Vol. 59, No. 4
419--430
EN
The origin of tilted disks in cataclysmic variables is explained in terms of a model involving the stream-disk interactions. Tilted, precessing disk causes periodically variable asymmetry in the irradiation of the two hemispheres of the secondary component, resulting in variable vertical component of the velocity of the stream. The following stream-disk interactions provide additional vertical acceleration to disk elements needed to produce and maintain disk tilt. Predictions based on this model compare favorably with observations.
19
Content available remote On the Amplitudes of Superhumps
Smak J.
Acta Astronomica
|
2009
|
Vol. 59, No. 1
103--107
EN
Amplitudes of bolometric light curves produced by 2D and 3D SPH simulations are used to determine the corresponding visual amplitudes. They turn out to be ≈10 times lower than typical amplitudes of superhumps. This means a major failure of the tidal model of superhumps.
20
Content available remote New Interpretation of Superhumps
Smak J.
Acta Astronomica
|
2009
|
Vol. 59, No. 1
121--130
EN
Observational evidence is presented for periodically variable irradiation of secondary components. This results in strongly modulated mass outflow. Superhumps are then due to enhanced dissipation of the kinetic energy of the stream. Qualitative interpretation of superhump periods and their variations is also presented.
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