Research Interests:
Results based on the 30 best nightly runs are reported. The moments of 33 brightness maxima and 35 minima show large scatter of phases within 0.6^p^-interval. The value of the primary photometric period of P=0.132953+/-13x10^-6^d differs... more
Results based on the 30 best nightly runs are reported. The moments of 33 brightness maxima and 35 minima show large scatter of phases within 0.6^p^-interval. The value of the primary photometric period of P=0.132953+/-13x10^-6^d differs from the previously published ones. Periodograms for detrended nightly runs show significant peaks at different frequencies from 28 to 103c/d. The most prominent peaks correspond to periods of 23.7, 15.2, 27.5 and 51.6min. This argues for transient quasi-periodic oscillations (QPO) occurring at few preferred time scales rather than for a QPO with a time scale decreasing from 27min in 1962 to 17min in 1985 (Semeniuk et al. 1987). Such behaviour may be explained by the "beat-frequency model" (Hollander & van Paradijs 1992). It seems that in TT Ari we observe contributions of several instability mechanisms with similar time scales. At higher frequencies 90-900 c/d the periodogram for all observations obeys a power law with an index gamma=1.60...
Research Interests:
Research Interests:
There is growing evidence that many Be stars are parts of binary systems. As the B-type primaries are very fast rotators and their spectral lines may be distorted by the circumstellar material, it is not easy to measure their radial... more
There is growing evidence that many Be stars are parts of binary systems. As the B-type primaries are very fast rotators and their spectral lines may be distorted by the circumstellar material, it is not easy to measure their radial velocity directly from the spectral lines. It has been shown that some Be binaries exhibit peak intensity variations consisting of double-peaked Hα lines that are phase-locked with orbital periods. We searched for such variations in the spectra of 12 Be stars, including several known and suspected binaries. Our results include confirmation of the orbital periods in ν Geminorum, ϵ Capricorni, κ Draconis, 60 Cygni, and V2119 Cygni, its refinement in o Puppis, as well as suggesting hints for binarity in o Aquarii, BK Camelopardalis, and 10 Cassiopeae. Monitoring of the Hα line profile variations in β Canis Minoris for over the last 10 years gives further support to the existence of a 182.5-day period found earlier in a smaller set of data. A similar but sti...
Research Interests:
Research Interests:
Research Interests:
Research Interests: Physics, Variable Stars, Astrophysics, Key words, Stars, and 7 moreBinary, Observatory, Individual, Variable, Sky, Oap, and Brightness
Research Interests:
We present results of two-color photometric study of the newly discovered EW– type eclipsing binary star GSC 04370-00206 in the field of the intermediate polar MU Cam. CCD V,R observations were obtained in the Astronomical Observatories... more
We present results of two-color photometric study of the newly discovered EW– type eclipsing binary star GSC 04370-00206 in the field of the intermediate polar MU Cam. CCD V,R observations were obtained in the Astronomical Observatories in Hlohovec, Baja and Kolonica in 2007-2009. Improved photometric elements for the primary minimum were determined: Min.BJD=2454805.75635+0.44264511(27)E. The range of the brightness variations is 13.79-14.13 (V) and 13.07-13.44 (R). The accuracy of the period determination is by a factor of ∼ 7, 000 times better than the one published by the discoverers based on only one night of observations. We report on the night-to-night variability of the shape of the light curve which is interpreted by a presence of spots in the atmosphere of one or both components (O'Connel effect).
Research Interests:
V Sge was studied on photonegatives of the Moscow and Odessa plate collections. ln consequence of us analysis of these observations and of the AFOEV data, the two types of long-time variability were distinguished: (l) outbursts with... more
V Sge was studied on photonegatives of the Moscow and Odessa plate collections. ln consequence of us analysis of these observations and of the AFOEV data, the two types of long-time variability were distinguished: (l) outbursts with characteristic time as ~212d ; (2) transitions between the high and low luminosity states with a cycle length ~250d; (3) variations with amplitude about 2m and smaller and at different time scales.
The method of "asymptotic parabola" fit is described, its analytical properties are discussed in comparison with other types of fits. The method is effective for the (possibly highly asymmetric) signals with practically linear... more
The method of "asymptotic parabola" fit is described, its analytical properties are discussed in comparison with other types of fits. The method is effective for the (possibly highly asymmetric) signals with practically linear ascending and descending branches connected by relatively short transitions at maximum or minimum, e.g. for the brightness variations of pulsating or eclipsing variables or for the phase variations in stars with abrupt period changes. The method is illustrated by an application to the Mira-type star U Her.
Research Interests:
Exactly 25 years ago, Santiago Tapia has detected circular and linear polarization of AM Her varying with the same period as the photometric and spectral characteristics. This had lead to a discovery of unprecedentedly exotic binary... more
Exactly 25 years ago, Santiago Tapia has detected circular and linear polarization of AM Her varying with the same period as the photometric and spectral characteristics. This had lead to a discovery of unprecedentedly exotic binary systems, in which the strength of the magnetic field is large enough to keep the white dwarf in a synchronism, dominating the accretion torque. Nowadays, about 70 representatives of this class of polars have been registered. We review the history of study of polars, starting with a "standard model", according to which, the red dwarf fills its Roche lobe and the is captured and channelized by a magnetic field of the white dwarf in the vicinities of the inner Lagrangian point. The models of the "propeller", "idling", "magnetic valve", "swinging dipole", "boiling asymmetric rainbow column" are reviewed, with a special attention to the unsolved problems of this study - contradiction between the obs...
Research Interests:
We report on a discovery of four new variable stars (USNO-B1.0 1234-0103195, 1235-0097170, 1236-0100293 and 1236-0100092) in the field of CL Aur. The stars are classified as eclipsing binary stars with orbital periods of 0.5137413(23) (EW... more
We report on a discovery of four new variable stars (USNO-B1.0 1234-0103195, 1235-0097170, 1236-0100293 and 1236-0100092) in the field of CL Aur. The stars are classified as eclipsing binary stars with orbital periods of 0.5137413(23) (EW type), 0.8698365(26) (EA) and 4.0055842(40) (EA with a significant orbital eccentricity), respectively. The fourth star (USNO-B1.0 1236-0100092) showed only one partial ascending branch of the light curves, although 22 nights were covered at the 61-cm telescope at the Sobaeksan Optical Astronomy Observatory (SOAO) in Korea. Fourteen minima timings for these stars are published separately. In an addition to the original discovery paper (Kim et al. 2010), we discuss methodological problems and present results of mathematical modeling of the light curves using other methods, i.e. trigonometric polynomial fits and the newly developed fit "NAV" ("New Algol Variable").
Research Interests:
Reminiscences on Prof. Vladimir Platonovich Tsessevich (11.10.1907-28.10.1983), the fa- mous scientist, lecturer and organizer of science are presented.
Methods for the determination of the orientation of accretion columns in magnetic cataclysmic variables based on the observations of the circular and linear polarization, X-Ray flux and profiles of emission lines are discussed. The... more
Methods for the determination of the orientation of accretion columns in magnetic cataclysmic variables based on the observations of the circular and linear polarization, X-Ray flux and profiles of emission lines are discussed. The non-uniformity of the density distribution through cross-section of the accretion columns leads to significant changes in the resulting spectra in two polarizational modes as compared with the 'homogeneous plasma slab' model. Simplified expressions for the circular polarization provides an additional relation between the inclination i and the magnetic latitude b. Similar relations ma e established from the X-Ray and spectral observations. However, by interchanging the values of i and b, one will obtain the same phase relationship. The only direct method obtain the true values for i and b is based on polarization position angle changes. Real columns are non-stationary and not axisymmetric, which significantly affect observe characteristics. Observa...
Research Interests:
The long term activity variations of polar QQ Vul in 1986-88 are reported. Changes of the amplitude and the shape of phase eclipse curve are present. Moments of 20 minima are presented which are in a good agreement with the ephemeris by... more
The long term activity variations of polar QQ Vul in 1986-88 are reported. Changes of the amplitude and the shape of phase eclipse curve are present. Moments of 20 minima are presented which are in a good agreement with the ephemeris by Andronov and Fuhrmann (1987, IBVS N 2976).
Research Interests: Astrophysics and Oap
Photometric analysis of photometric variability of the semi-regular pulsating variable U Del is analyzed. From the international AFOEV database, 6231 brightness values in the time interval JD 2451602-55378 were chosen. For the periodogram... more
Photometric analysis of photometric variability of the semi-regular pulsating variable U Del is analyzed. From the international AFOEV database, 6231 brightness values in the time interval JD 2451602-55378 were chosen. For the periodogram analysis, we have used a trigonometric polynomial fit. Using the criterion of minimal variance of the approximation at arguments of observations, the optimal degree is s=1. Initial epoch for maximum is T0=JD2453340±3, the period P=1198±4d. Mean brightness at maximum is 6.624±0.005, at minimum 7.124±0.005, i.e. the amplitude is 0.499±0.005m. Besides this slow variability, there is a faster oscillation of a period of 119.45±0.06d, amplitude 0.303+0.005m and an initial epoch for maximum 2453215.1±0.5. These results are mean during the time interval after that analyzed in the catalogue of Chinarova and Andronov (2000). Also the method of "running sines" with a filter half-width Δt=0.5P. The local mean (averaged over a short period) brightness...
Research Interests: Mathematics, Physics, Astrophysics, Stars, Individual, and 4 moreVariable, Pulsating, Amplitude, and Brightness
We perform the CCD (R) photometry of the nova-like variable V603 Aquilae (Nova Aquilae 1918) during 7 nights in 1999. The star showed quasi-periodic oscillations (QPO) with cycles ranging from 03035 to about 09055, and... more
We perform the CCD (R) photometry of the nova-like variable V603 Aquilae (Nova Aquilae 1918) during 7 nights in 1999. The star showed quasi-periodic oscillations (QPO) with cycles ranging from 03035 to about 09055, and "positive" superhumps with a photometric period of 014443? days. The "A- scalegram" analysis shows evidence for QPOs with an effective period P : 17.6 minutes and an amplitude of 23 mmag.
Physical mechanisms and corresponding mathematical models for different types of stellar variability are reviewed with applications to concrete stars. Special attention is attributed to the following topics: cataclysmic variables... more
Physical mechanisms and corresponding mathematical models for different types of stellar variability are reviewed with applications to concrete stars. Special attention is attributed to the following topics: cataclysmic variables (synchronous and synchronizing magnetic systems, non-magnetic novalike stars, dwarf novae; magnetic activity of the red companion, third body around), pulsating variables (additional classification criteria of variability, multiparameter correlation analysis of the characteristics of the mean light curves of groups of long-period stars and of the multi- parameter correlation analysis of the individual characteristics of their pulsations), mathematical models (multi-periodic, multi-harmonic, multi-shift variations with possible trends, mono- and multi- cyclic variations of low coherence and the frequency changing/switching signals, "red noise" variability. Some original papers and links may be found at http://ila.webjump.com
Research Interests:
Analysis of the spectral sensitivity of the CCD camera ST-4 is presented. The half-maximum sensitivity range is 685930 nm. Mean wavelengths λ1 = λ = 796 nm, and λ 2 = (λ -1)-1 = 730 nm are measured. Eclipses of PX And were detected at HJD... more
Analysis of the spectral sensitivity of the CCD camera ST-4 is presented. The half-maximum sensitivity range is 685930 nm. Mean wavelengths λ1 = λ = 796 nm, and λ 2 = (λ -1)-1 = 730 nm are measured. Eclipses of PX And were detected at HJD 48861.3933 and .5393.
Results of the international observational campaign "TT Ari-98" are presented. Altogether 11 336 observations have been obtained in the "positive superhump" state during 18 runs in 6 observatories, partially in UBV,... more
Results of the international observational campaign "TT Ari-98" are presented. Altogether 11 336 observations have been obtained in the "positive superhump" state during 18 runs in 6 observatories, partially in UBV, UBVR (switching filters). During one night, 1027 simultaneous UBVRI data have been obtained. No significant shifts between the times of extrema in different colors have been found. The asymmetry is 0.44±0.01 is present showing more abrupt brightness increase than a decrease. The smoothed U-B color varies from -0m.65 to - 0m. 86, whereas the B-V=0m. 03 is remarkably constant. Sometimes the maxima have larger amplitude and a sharp shape corresponding to areas with a duration of ∼ 5 minutes. One may note a significant decrease of the mean magnitude by 0m. 35 on JD 2251069. The moments of 21 maximum and 18 minima are listed. They correspond to the period for the 1997 data obtained by Skillman et al. (1998) showing no period change from one season to the n...
Research Interests:
We propose a set of the photometric parameters which could be useful for the classiffication of the pulsating Mira-type stars and related objects and determination of the EAGB and TPAGB stages of the stellar evolution. To solve this... more
We propose a set of the photometric parameters which could be useful for the classiffication of the pulsating Mira-type stars and related objects and determination of the EAGB and TPAGB stages of the stellar evolution. To solve this problem, the light curves of faint Mira-type stars and of the semi-regular variable V411 Sct were approximated using the program FDCN, which computes a trigonometric polynomial of a statistically optimal degree (I.L.Andronov, 1994, 2003). The at las of statistically optimal fits of the phase curves of 34 long-period is presented, based on digitized data from the scanned "Atlas" by P. Maffei and G.Tosti (http://astro.fisica.unipg.it/atlasmaffei/main.htm). Some statistical relations between the parameters of the trigonometrical polynomial approximation of the phase curve are analyzed. for an additional criterion of detailed classiffication of long-perodic variables, we used various parameters, e.g. "period", "amplitude", &quo...
Research Interests:
A program WWZ is introduced, which realizes the wavelet analysis using an improved modification of the algorithm of the Morlet wavelet for a general case of irregularly spaced data, which is typical for the databases available in virtual... more
A program WWZ is introduced, which realizes the wavelet analysis using an improved modification of the algorithm of the Morlet wavelet for a general case of irregularly spaced data, which is typical for the databases available in virtual observatories. Contrary to the well-known analogs, working with regularly spaced (equidistant in time) arguments, we have implemented an improved algorithm presented by Andronov, (1998KFNT...14..490A, ..conf...57A), which significantly increases the signal-to-noise ratio. The program has been used to study semiregular pulsating variable stars (U Del et al.), but can be used the analysis of signals of any nature.
Research Interests:
Some algorithms and programs are described for determining the parameters of processes with constant and variable periods. Those are: FOUR-1 periodogram analysis by using the least squares one-harmonic fit, FOUR-N corresponds to a number... more
Some algorithms and programs are described for determining the parameters of processes with constant and variable periods. Those are: FOUR-1 periodogram analysis by using the least squares one-harmonic fit, FOUR-N corresponds to a number of harmonics, FOUR-T to a sine wave with a linear trend, FOUR-M to a number of waves with independent frequencies. Multishif-ted and mean weighted periodograms are discussed. PERMIN allows the determination of a best fit period from the moments of "characteristic events" only. The programs allows one to determine not only the parameters, but accuracy estimates and the " false alarm" probability as well. Some applications of these and some other methods to variable stars of different types are discussed.
Research Interests:
The light curves show very large even for polars night-to-night variability of the amplitudes (from 0.4m to 1.6m) and shapes. The flares may be owed not only to the inhomogeneous accretion, but possibly some to the UV-Cet events. Large... more
The light curves show very large even for polars night-to-night variability of the amplitudes (from 0.4m to 1.6m) and shapes. The flares may be owed not only to the inhomogeneous accretion, but possibly some to the UV-Cet events. Large scatter of the phases does not allow to fit all observations even with one period, arguing for future monitoring.
Research Interests: Physics and Astrophysics
Abstract Methods for time series analysis (TSA) are reviewed. Special attention is paid to multicomponent signals with irregularly spaced arguments, what is typical for geoscience and astronomy. Examples are the satellite photometrical... more
Abstract Methods for time series analysis (TSA) are reviewed. Special attention is paid to multicomponent signals with irregularly spaced arguments, what is typical for geoscience and astronomy. Examples are the satellite photometrical surveys (GAIA, KEPLER, HIPPARCOS/TYCHO, WISE, TESS, etc.), ground-based CCD projects (CRTS, SuperWASP, NSVS, ASAS, OGLE, ZTF, etc.), and collections of photographic negatives (Harvard, Sonneberg, Odessa, etc.). Even for “continuous” time series without gaps, the duration of observations is generally not equal to an integer number of periods. In this case (and many others), the basic functions are not orthogonal, so common simplified methods give biased parameters of the approximations. We review improved algorithms and programs (including our own) for statistically correct analysis, and illustrate results for real and model data.
Research Interests:
Research Interests:
Time series analysis of the bright cold carbon SR-type star Y CVn was studied. The star belongs at a rare subclass "J" and has a separate asymmetric envelope. It is assumed that no "s" pro- cess takes place in this... more
Time series analysis of the bright cold carbon SR-type star Y CVn was studied. The star belongs at a rare subclass "J" and has a separate asymmetric envelope. It is assumed that no "s" pro- cess takes place in this star. Due to this, Y CVn may belong not to the AGB, but to the RGB stage, or to a stage of helium burning in a nucleus after a helium flash. The data from the published international databases of AFOEV (France) and VSOLJ (Japan) were studied using the periodogram and wavelet analysis and the \running sine" approximation. The cycle of variations is 267 d (varying from 247 d to 343 d which are superimposed on 1000 d -10000 d waves.
Research Interests:
Research Interests:
Cyclic period variations (P ≈ 19400d) in T Cep were investigated. As the result of cross-correlation analysis, relations between individual cycle parameters were found. Relations between period–amplitude, hump–amplitude, hump–minimum... more
Cyclic period variations (P ≈ 19400d) in T Cep were investigated. As the result of cross-correlation analysis, relations between individual cycle parameters were found. Relations between period–amplitude, hump–amplitude, hump–minimum magnitude, and others have been obtained.
Research Interests:
A synopsis of mathematical models describing different types of variability and their application to some classes of stars is given.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Physics and Astrophysics
Dans les systemes binaires magnetiques on peut observer des disques d'accretion qui sont formes par l'ejection de matiere de l'etoile secondaire vers la naine blanche en rotation rapide. Dans certains cas cette rotation... more
Dans les systemes binaires magnetiques on peut observer des disques d'accretion qui sont formes par l'ejection de matiere de l'etoile secondaire vers la naine blanche en rotation rapide. Dans certains cas cette rotation n'est pas synchronisee avec le mouvement orbital et de la matiere peut etre ejectee vers l'exterieur. On propose ici un nouveau modele pour de tels disques d'excretion