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Several powerful outbursts have been observed during many years of observations of the symbiotic object MWC 560. The last active stage began in the autumn of 2018 and continues to the present. Observations of this event began at the Fesenkov Astrophysical Institute at the beginning of 2019. In our previous article we published the results obtained in early 2019. A light curve of the object and emission line profiles are presented; it is noted that a broad absorption band formed in a high velocity collimated jet vanishes. In this article we present the results of further spectral and photometric observations of MWC 560. It is to be noted that in 2021 the brightness of this object is sustained at a high level exceeding that obtained during the previous outbursts. In addition, at the end of 2020 a tendency toward a gradual weakening of the radiative fluxes in the emission lines was remarked. The profiles of all the lines have absorption components shifted to the “blue” by 52±5 km/s. It may be assumed that during this outburst there was partial (or complete) destruction of the accretion disk, so that the source of the high velocity collimated jet vanished. The gradual reduction in the radiative fluxes in the emission lines may be caused by a drop in the power of ionizing radiation.

We present the first photometric observations and light curve modelling of the discovered systems GSC 01870-00458 and USNO-A2.0-0975 04721840. Our modelling was carried out using a recent Windows interface version of Wilson and Devinney code based on model atmospheres provided by Kurucz. The accepted models revealed absolute and physical parameters that can be used to study the evolutionary states of systems. The parameters show that primary component is more massive and hotter than the secondary component for both systems, and spectral types of the system components were adopted. Locations of both systems on theoretical mass-luminosity and mass-radius curves revealed a good fit for components of both systems except for the secondary component of the system GSC 01870-00458.

New observational data on the last two outbursts of the EXor star V1118 Ori are presented. The combined light curve of the last outburst is derived and fitted. The dates of the start of the outburst, its maximum, and end, as well as the maximum magnitude, and the rates of increase and decrease of the brightness were determined.

Published data indicate a substantial increase in the differential rotation parameter ∆Ω of stars hotter than 6700 K. By analyzing the shape of the light curves and the presence of a specific set of peaks in their power spectra, we have found that 47 of 57 objects with Teff greater than 7500 K that were studied can be identified as pulsating stars and only 10, as stars with brightness variation owing to rotational modulation. After eliminating the pulsating variables, for the stars with Teff greater than 7500 K the average value of ∆Ω= 0.051±0.01 rad/day. This conclusion conflicts with our earlier assumption that the peaks in the power spectra for ROTD stars are caused by a possible manifestation of differential rotation. Further independent evidence for a low value of ∆Ω for stars in spectral class A has been obtained from Zeeman-Doppler charts for the star γ Gem, with an estimate for the differential rotation parameter of the star of 0.0073±0.0023 rad/day.

RY Sct is a unique massive binary star system in a short transitional evolutionary phase. It is an eclipsing binary where both stars have overfilled their Roche cavities, so that the system is in an “overcontact” state. It is surrounded by a young circumstellar nebula. The binary is regarded as a rare progenitor of a type WR+OB system. RY Sct is close to the Eddington luminosity limit, so that radiative pressure plays an important role in mass loss. At least one of the components of the close binary may be associated with a rare class of LBV stars or the so-called S Doradus variables. We have calculated the orbital elements using the old photometric data of Zakirov and Kumsiashvili and new spectral data, together with an analysis of HST observations. A model was examined according to which the components of RY Sct are in an overcontact state and fill their Roche cavities. The brighter primary component transfers mass to the more massive but less bright secondary. The binary system is surrounded by a common envelope. As initial parameters we, chose a mass ratio q = 4.42 and orbital period P = 11d.12471, and used an orbital inclination of i = 75.6°.

In the present paper we use a complete set of CCD observations to model the light curves of the new W UMa systems, GSC 4835-1716 and USNO-A2.0_1275-10813091. The light curve modeling is performed by means of the W-D code where Kurucz (1993) model atmospheres are implemented. We treated the asymmetry of the observed curves using a spotted model. Physical parameters of the accepted model revealed that primary components of the studied systems are massive and hotter than the secondary ones. The components of the system GSC 4835-1716 are found to be on or near the TAMS track while the components of the system USNO-A2.0_1275-10813091, lie between the ZAMS and TAMS evolution tracks.

The extragalactic radio source OJ 287 is one of the most studied blazars. A huge amount of data has been accumulated on it (for more than 40 years in the radio range and more than 100 in the optical). Studies of the rapid variability in the radio flux and stellar magnitude of this object with characteristic times ranging from a few hours to several days are of interest in connection with the possible presence in this radio source of a system of binary black holes that includes a central object and its satellite. Here we present the results of searches for and studies of the intraday variability (IDV) and interday variability of the radio source OJ 287 (March-May 2019) at frequencies of 6.1 and 6.7 GHz on the telescopes at VIRAC (Ventspils International Radioastronomy Center, Latvia) compared with optical V, R, and I band variability (April-May 2019). Optical light curves were obtained on the 1.2-m Schmidt system telescope at the Baldone Astronomical Observatory, Latvia, on the 1-m VNT telescope at the Vihorlat Astronomical Observatory, Slovakia, and on the AZT-3 telescope at the Mayaki Observational Station of the I. I. Mechnikov Odessa National University, Ukraine. Similarities are found in the long-term quasiperiods in the radio (15, 42 days) and optical (13, 36-37 days) ranges. The minimum characteristic time for changes in the flux density was 1.4 hours and 0.6 hours at frequencies of 6.7 and 6.1 GHz with fundamental quasiperiods of about 5 and 2-3 hours during different observation sessions. The results obtained here are compared with those of other authors.

In the present paper, we obtained the first orbital solution for the newly discovered W UMa systems: GSC 3983-0544 and GSC 4502-1040. We used the most recent version of the Wilson-Devinney code to model the light curves of the two systems. The spectral type of the components of the two systems was adopted and the accepted solutions revealed some absolute parameters, which enable us to draw a preliminary picture of their evolutionary status.

The rotational and flare activity of the chemically peculiar star B9.5IIIpHgMnSi βScl is studied using data from the archive of the TESS space mission. Rotational modulation of the brightness is clearly visible in the light curve of this star, along with two flares that have a structure typical of flares in stars of a later spectral class, with a sharp rise, a peak, and a damping stage. The constructed power spectrum has a peak corresponding to a rotation period of 1.91±0.09 days. The standard technique for analysis of the flare activity of stars based on observations from the Kepler space telescope and the TESS mission yields the energy of the radiation in the two flares. The energy emitted in the first flare was 3·1036 erg and in the second, 4.5·1035 erg. The values we have found agree with published estimates for the first flare. Arguments in favor of and against the flares taking place on βScl, rather than on a possible companion at an angular separation of 0.641 arcsec, are discussed.

Results of photometric observations of the Seyfert galaxies NGC 3516, NGC 5548, NGC 3227, NGC 4051, NGC 4151 and NGC 7469 made on the east 1-m telescope (Tyan-Shan Astronomical Observatory of the V. G. Fesenkov Institute of Astrophysics) are presented in this paper. The observations were made in the three filters BVR, from April 9, 2014 for NGC 3516, NGC 5548, and NGC 3227, and since 2013 for NGC 4051, NGC 4151 and NGC 7469. The observational data yielded estimates of the brightness of the central regions of the Seyfert galaxies and light curves were plotted.

New BVRI light curves of the W UMa type eclipsing binary of multiple system 1SWASP J093010.78+533859.5 (GSC 0380-00759) have been constructed based on CCD observations obtained using 1.88 m reflector telescope of KAO, (Kottamia Astronomical Observatory), Egypt on March, 20th in 2013. New times of minima and new ephemeris have been determined from these light curves. Using the Binary Maker 3.0 (BM3) and PHOEBE program, the geometric and photometric element parameters of this system have been derived. Light curve analysis results indicate that J093010B is an overcontact binary with third body shared with 0.056 ± 0.006 of its total luminosity. The filling factor of the system is approximately equal to 17%. According to all available eclipse timings, the preliminary rate of period change has been determined to be -6.35 x 10-5 day/yr. The semi-major axis has been determined as 1.6 ± 0.1 R ⊙.

The symbiotic object EG And consists of a giant star (M4III) and a white dwarf. Numerous studies of this object show that its light curve has two minima. There are different hypotheses regarding the source of the secondary minimum, but the problem has not yet been solved. In this paper we present data from photometric and spectral observations of EG And during 2009-2018: B, V, and R magnitudes in the Johnson system and fluxes in the Hβ and Hα emission lines. An analysis of these data showed that the emission fluxes correlate with the orbital phase. The highest fluxes are observed near the secondary minimum. At the same time, emission fluxes are still observed in the primary minimum but attenuated by roughly a factor of 7-10. This indicates that the size of the ionized zone exceeds that of the giant star. On the whole, the light curve for 2009-2018 is consistent with previous photometric data. Rapid (over a few minutes) fluctuations in the brightness of this object are detected in the V and R bands with amplitudes of ~0m.15 and 0m.35, respectively.

The optical variability of stars in the KP2001 catalog is studied. Monitor data from the automatic Northern Sky Variability Survey (NSVS) are used for this purpose. Of the 257 objects that were studied, 5 are Mira Ceti variables (mirids), 33 are semiregular (SR), and 108 are irregular variables (Ir). The light curves of the other objects show no noticeable signs of variability. For the first time, 11 stars are assigned to the semiregular and 105 stars to the irregular variables. Of the irregular variables, the light curves of two, No. 8 and No. 194, are distinct and are similar to the curves for eclipsing variables. The periods and amplitudes of the mirids and semiregular variables are determined using the “VStar” program package from AAVSO. The absolute stellar magnitudes M K and distances are also estimated, along with the mass loss for the mirids. The behavior of stars from KP2001 in 2MASS and WISE color diagrams is examined.

A comparative analysis of the special shapes (patterns, profiles) of the eclipses applied for the phenomenological modeling of the light curves of eclipsing binary stars is conducted. Families of functions are considered, generalizing local approximations (Andronov, 2010, 2012) and the functions theoretically unlimited in a width, based on a Gaussian (Mikulasek, 2015). For an analysis, the light curve of the star V0882 Car = 2MASS J11080308 - 6145589 of the classic Algol - subtype (\beta Persei) is used. By analyzing dozens of modified functions with additional parameters, it was chosen the 14 best ones according to the criterion of the least sum of squares of deviations. The best are the functions with an additional parameter, describing profiles, which are limited in phase., Comment: 15 pages, 3 figures

Polarimetric UBVRI observations of the Nova V339 Del during the 5-108 days following the maximum of the outburst of 2013 reveal a variability in the degree of linear polarization with an amplitude of about 0.2%. The character of the variability in the polarization parameters during the period up to 30 days after the maximum is indicative of a nonspherical diffuse shell, with a geometry that is more likely bipolar than disk-shaped. In the early nebular stage (30-100 days after the maximum) a variability in the position angle of the intrinsic polarization was observed that suggests that the shape of the shell deviates from axial symmetry.

Results are reported from multicolor photometric observations of the SU UMa-type dwarf nova 1RXS J003828.7+250920 in 2011, roughly a year after the super-outburst of 2010, and in 2012, when the object was in a quiescent state and underwent an outburst. Partial eclipses were observed in the system with depths of about 0m.6 in all color bands, both in the quiescent state and during the outburst. The orbital period of the system, 0.09451001(4) days, was determined for the first time and identifies the object as a dwarf nova in the “gap” in the orbital-period distribution of the cataclysmic variables. The ephemerides for the middle of the eclipse are determined. The average light curve profile resembles the “classical” light curve of U Gem. The orbital periodicity in the brightness variations of 1RXS J003828.7+250920 coexists with another signal with a period of 0.092 days, which we interpret as a period of negative superhumps. The color temperatures derived from the color indices may indicate multicomponent emission from 1RXS J003828.7+250920 by sources which appear to be hot and cold parts of the accretion disk and a hot spot on the accretion disk.

We have analyzed photometric UBV light curves of the massive eclipsing binary system V729 Cyg which lies in the Cyg OB2 stellar association. The observations were made at the Abastumani Astrophysical Observatory in 1983–2003 as part of a program for studying binary systems of early types. The system V729 Cyg is a spectroscopic binary and consists of Of-stars. Effects associated with the collision of stellar winds are observed in it. Various researchers have assumed previously that the binary system is at an evolutionary stage of conversion into a WR+O system. The light curves have been analyzed by a synthesis method in terms of a Roche model using our own computer code analogous to the standard Wilson-Devinney code. This analysis shows that the binary system has a contact configuration and an orbital inclination of about 66 degrees. The absolute parameters of the components are estimated to be M 1 = 30.4M ⨀ , M 2 = 9.2M ⨀, R 1 = 24.6 R ⨀ , and R 2 = 13.8R ⨀ .

In 2010-2011 high precision CCD observations were made of the new eclipsing variables GSC 4277 0586 and GSC 4481 0230 and their light curves were analyzed. The photometric elements were calculated. A comparison of the longitude angles in different epochs showed that the line of apsides of the GSC 4277 0586 system may have a negative rotation of $$ {\overset{.}{\upomega}}_{obs} $$ = −0.8 ± 0.5o /year. This result is based on a small difference between the epochs of the observations, so it is preliminary. The motion of the orbit is quite fast, so that, in order to verify this result, it is sufficient to obtain new light curves and calculate a new value for the longitude of the periastron. An analysis of the light curve for the binary system GSC 4481 0230 showed that the longitude of the periastron of its orbit is very close to 360°. The expected theoretical value for this system is $$ {\overset{.}{\upomega}}_{th} $$ ≤ 0.2o /year. A reliable determination of the orbital rotation speed of this star will require an interval of at least a few decades between observations.

We present moderate resolution CCD spectra and R photometry for seven KP2001 stars. We revised the spectral classification of the stars in the range 3900 - 8500 A. On the bases of light curves of the NSVS (Northern Sky Variability Survey) database we classify KP2001-18 as a semi regular and KP2001-176 as Mira type variables. For all observed objects NSVS phase - dependence light curve analysis and variability type classification was performed with the VStar Software. Using period luminosity relation we computed MK magnitudes and the distances to variables., Comment: Nine pages, six figures, in press on Astrophysics (Astrofizika)

Results are presented from many years of photometric (VRCIC) observations of three variable T Tauri type stars in the cluster IC 348: V712 Per, V719 Per, and V909 Per. All three stars have photometric activity characteristic of UX Ori stars. The activity of V719 Per has increased significantly over the last 10 years: the amplitude of its Algol-like minima has increased by roughly a factor of 4 and has reached three stellar magnitudes in the I band. Periodograms of the light curves do not confirm the periods found previously by other authors on the basis of shorter series of observations. The slope of the color tracks on “color-magnitude” diagrams is used to determine the reddening law for these stars owing to selective absorption by circumstellar dust. Modelling of these parameters by the Mie theory shows that the maximum size amax of the dust particles in the protoplanetary disks of these stars is 1.5-2 times greater than in the interstellar medium. In V712 Per and V909 Per, the bulk of the mass of the dust particles is concentrated near amax, while in V719 Per the average mass of the dust particles is determined by the minimum size of the particles. It should be emphasized that these conclusions rely on an analysis of the optical variability of these stars.

Three-color photoelectric observations of the early spectral-type eclipsing binary system W Sct, made for the first time at the Abastumani Astrophysical Observatory, are reported. The light curves of W Sct are unstable and asymmetric, with a maximum after the first minimum that is brighter than the second maximum. The spread in the data exceeds the measurement errors. The observed light fluctuation are caused by physical conditions in this system. It is clear that mass transfer has played an important role in its evolution.

We have made high accuracy CCD observations of the eclipsing binary star GSC 4477 0347 during 2009-2013 and obtained light curves. The photometric parameters and elements of the orbits, and the ephemerides of the primary and secondary minima have been obtained. The longitude angles of the orbital periastron obtained for different observational seasons have been used to calculate the apsidal motion: 𝜔obs = 2.28 ± 0.04° /year. This is a factor of 1.5 faster than the theoretical value calculated for the primary lifetime of the component stars, which are class B8V + B9V on the Main sequence. Either we have actually found the stars within a short segment of their times of entry into the Main sequence or the apsidal motion is affected by the presence of a third body in the system, as indicated by a “third” light in the solution of the light curves ( L3 ≈ 10 % ≈ of the brightness of the entire system).

A two-dimensional classification of thirteen stars from the KP2001 catalog is described. CCD spectra of these stars were obtained at the 2.6-m telescope of the Byurakan Observatory with the SCORPIO and Byu FOSC2 spectral cameras. The classification employs methods based on the depression bands of the TiO and CaH molecules, as well as absorption lines of FeI, the NaI D lines, a BaII ion, the Hα line, and others. The luminosity classes were determined using the CaH band with a minimum depression depth observed at λ 6975A. The results of the classification are given in Table 1. The subclasses of the stars range from M5 to M10 and the luminosity classes, from supergiants (I) to giants (III). Since the KP2001 stars are close to the plane of our galaxy, interstellar absorption was taken into account and they fall in the LPV region on a (J-H), (H-K) diagram. The stars KP2001-6, 7, 70, and 230 are variable, as confirmed by the behavior of their light curves taken from the NSVS data base. Of these, KP2001-6, 7, and 70 are semiregular (SR) variables and KP2001-230 is a Mira variable. The variability of this last star was revealed in 2003 on photographic plates from a year apart (the difference in the photographic magnitudes was 1m.2).

The variations in the radius of the accretion disk of the WZ Sge dwarf nova OT J213806.6+261957 are estimated. The calculations are based on photometric observations of the object during a superoutburst that began on May 6, 2010. Shortly after the maximum, superhumps typical of WZ Sge stars appeared in the light curve of OT J2138. Photometric observations of the object between May 15 and December 2, 2010, reveal a variability in the period of the superhumps, so that it is possible to track the changes in the radius of the accretion disk during the superoutburst in terms of a model of tidal instability in the accretion disks of dwarf novae. It is shown that the radius of the accretion disk can exceed both the radius of the 3:1 resonance and the radius of the tidal effect from the secondary component.

The eclipsing variable GSC 4513 2537= V1176 Cas is a recently discovered binary system. We have made high precision CCD observations of it during 2009-2010 and obtained light curves. The photometric parameters and orbital elements, periods of the primary and secondary minima, and U, B, and V magnitudes have also been obtained. The rate of rotation of the apsidal line is estimated to be $ {{\dot{\upomega}}_{obs }} $ = 0.08 ± 0.04 / year. This is 5 times the theoretically predicted $ {{\dot{\upomega}}_{obs }} $ = 0.016 ± 0.005 /year. The bulk (80%) of the theoretical rate of rotation of the orbit is in the relativistic component. Unfortunately, the accuracy of the observed rate of orbital rotation of the orbit is low, so getting a more reliable result will require repeating this study in a few years.

Photometric and high-resolution spectral data on the Be Herbig star HD 52721 from our earlier article [1] are supplemented by new data obtained with an echelle spectrograph mounted on the 2.1-m telescope at the San Pedro Martir Observatory (Ensenada, Mexico). BVR photometry data obtained during 1987-1998 at the Maidanak Observatory (Uzbekistan) are also examined in more detail. This confirms that the phase light curve for an orbital period P = 1d.610 has two minima with different depths separated in phase by 0.5, and reveals a reddening of the object at the phases of the minima. The profiles of atmospheric He I lines in the 4000-4500 A range are found to be broader, shallower, and more asymmetric at the brightness maximum than at the minimum, as expected in close binary systems. Various factors which may influence the formation of the observed atmospheric line profiles are discussed. The observations confirm the hypothesis of a dense disk shaped gas envelope surrounding the system that makes a significant contribution to its overall brightness and contains a global azimuthal inhomogeneity rotating in synchrony with the orbital motion of the system components. We emphasize the need for new photometric observations of HD 52721 in the region of the atmospheric lines, as well as a continuation of the photometric program, in order to confirm the existence of and to analyze the stable, small variations in the light curve of this object.

The shape of the light curves, behavior of the MgII h and k and MgI (2852 A) emission lines, and polarization of the light in different phases of the brightness variation of the mirids are examined. Studies of these characteristics of the mirids confirm earlier results. An analysis of the light curves shows that almost all Mira Cet stars have a hump in the middle of the rising branch of the light curve. This structure is presumably a consequence of the binary nature of the star. Noteworthy new results include a periodic variation of these emission lines during the inverse phases and a dependence of the width of the MgII h and k lines on stellar magnitude. An analysis of more than 400 polarimetric measurements shows that the maximum polarization of individual stars is observed during phases from φ = 0.6 to 0.8, and for a synthetic mirid at phase φ = 0.7.

The galaxy Mrk 501 was observed with the GT-48 twinned atmospheric Cherenkov telescope over 9 moonless nights during May-June 2006. About 9 hours of observation time for the source, in good weather, were used to separate γ-ray showers from background showers. Excess γ-like events were detected with a significance of ~6σ. The flux was estimated assuming a Crab-like spectrum for Mrk 501 at energies E > 350 GeV using data from quasi-simultaneous observations with the Whipple telescope. The source was in a state of low activity in the TeV range, as confirmed by observations at other Cherenkov telescopes. Although the light curve of this object according to ground based observations manifested no significant variations on a diurnal scale, the soft and hard X-ray data indicate that the largest amplitudes of the variations occur at the lowest energies.

In a prolonged study (about 30 years) of the photometric activity of WW Vul we have discovered unusual eclipses in the light curve of this star. They last 2-3 years and repeat with a period of 13.9 years. One nontrivial feature of these eclipses is that in their deepest part the star’s brightness increases. Changes in the color indices during these events indicate that the brightening of the star is caused by reduced extinction in the center of an extended gas-dust structure that periodically intersects the line of sight. Possible mechanisms for these eclipses are discussed briefly.

Results from three-color photoelectric observations of the early-spectral type eclipsing-binary system V729 Cyg at the Abastumani Astrophysical Observatory are presented. These observations, the first for this star, covered the secondary maximum quite well and revealed a displacement of Max II to a phase of 0.80. There is reason to suspect that this phase shift reflects increasing activity of a mass flux in a common envelope. The light curves of V729 Cyg are unstable and asymmetric, and thereby create a maximum after the second minimum that is brighter than the first maximum. The spread in these points exceeds the measurement error. The observed fluctuations in the brightness are caused by the physical conditions in this system. There is no doubt that mass transfer has played an important role in the evolution of this system.

This is a study of the cataclysmic variable HS 0218 + 3229. An analysis of 2000 CCD and 200 photographic observations of this close binary system from 1963-2010 reveals two outbursts (in 1980 and 2007) with amplitudes of about 4m in the pg and V bands. This variable has been classified as a UGSS-type dwarf nova with rare, symmetric outbursts, which are typical of “inside-out” outbursts. The orbital period is found with greater accuracy to be 0d.2973559, during which a double wave is observed owing to the ellipsoidal shape of the secondary component— a class K5V star. The phase light curves and color index curves are introduced and explained, and an interpretation of the position of the object in two-color diagrams is provided. A difference in the orbital light curves before and after the outbursts is detected, and some physical characteristics of this close binary system are determined.

Results are presented from photometric studies of the dwarf nova V1108 Her conducted at the primary focus of the 2.6-m G. A. Shajn Telescope at the Crimean Astrophysical Observatory during June-July 2008, 4 years after the 2004 outburst. An orbital period of 0.05672(4) days is found for the system. An analysis of observations made earlier during the 2004 outburst reveals an orbital signal which indicates that V1108 Her is an eclipsing system. The mass ratio of the secondary component to the white dwarf is estimated to be q = 0.068, which makes it highly likely that the secondary component of this system is a brown dwarf. The orbital light curves indicate a complex structure for the accretion disk whose radius has reached a 2:1 resonance. An explanation is suggested for a quasi-periodic modulation in the brightness at 1/4 of the orbital period observed in V1108 Her and other WZ Sge systems.

Photometric and high resolution spectroscopic data for the Herbig star HD 52721 obtained from October 2009 through October 2010 are presented. We confirm the cyclical character of the photometric variability of HD 52721 discovered previously by others. The variability shows up as minima in the light curve of this star which repeat with a period P = 0d.805 and are typical of eclipsing binary systems. ASAS data covering an observation period from September 2003 through December 2009 show that two neighboring photometric minima differ from one another, and the actual orbital period of the system must be twice as high (P = 1d.610). This is confirmed by the spectroscopic data. These show that the center of gravity of the emission Hα line and the profile of the HeI 6678 line with a distinct, bright circumstellar component have a clear correlation with a period of 1d.610. To all appearances, HD 52721 is a close binary system consisting of two class B2 stars with quite similar parameters. We propose that the observed cyclical variations in the circumstellar parameters may be related to the existence of a global azimuthal inhomogeneity within the shell which rotates synchronously with the orbital motion of the system components.

Results are reported from a study of the variability of the x-ray and very high energy (VHE) γ -ray emission from Mrk 421 during a 10-day period of enchanced source activity at the end of 2005. The TeV data were taken from observations with the Whipple 10-m Cerenkov telescope and the soft x-ray data, from the ASM on board the RXTE orbital observatory. Light curves for this source indicated an obvious variability in the form of flares in both energy ranges. During the flares, the flux of VHE γ -rays exceeded that from the Crab nebula and correlated positively with the observed x-ray emission. The flux of VHE γ - rays varied almost linearly with the soft x-ray flux. The statistical characteristics of the variability were independent of energy and the two emission components were detected quasi-simultaneously. The observed temporal properties of the source can be interpreted in terms of the rapid acceleration of leptons in a jet using a synchrotron self-Compton model. Our studies confirm a flare activity intrinsic to this source on the scale of a day found in earlier studies.

The photometric activity of the star BF Ori, which belongs to the family of UX Ori-type stars, is studied. New data obtained with the ASAS robotic telescope confirm the existence of a cyclical component in the light curve for this star with a duration of roughly 11-12 years. The form of the photometric cycle resembles the theoretical light curves for a young binary system with a low-mass secondary component, and which is accreting matter from a surrounding common disk. Alternative mechanisms for the cyclical variability of UX Ori stars are also discussed.

A modified spectral analysis technique is used to study the temporal structure of the emission from the γ-ray burst GRB 080319B detected in three space missions, Swift/BAT, Wind/KONUS, and Integral/SPI ACS. The energy range of the γ rays detected in these experiments covers 15-10000 keV. The time resolution for the first two of these experiments was 64 ms and for the third, 50 ms. Quasiperiodic oscillations with periods from 0.6 s to 6 s were observed. To within the time resolution, the oscillations with periods of 1.28, 0.89, and 0.64 s are the second, third, and fourth harmonics, respectively, of oscillations with a period of 2.56 s, while oscillations with a period of 0.96 s are the third harmonic of oscillations with a period of 2.94 s. The behavior of the quasiperiodic components is examined as a function of the phase of the events. Possible physical mechanisms for the quasiperiodic oscillations in the light curves of γ-ray bursts are discussed.

We present moderate resolution CCD spectra and R photometry for seven KP2001 stars. We revised the spectral classification of the stars in the range λλ4000−8700A . Our photometric data confirmed the behavior of the light curves downloaded from the NSVS (Northern Sky Variability Survey) database. For KP2001-32, presented as a Mira-type variable in NSVS, we estimated absolute bolometric M b and K-band M K magnitudes as well as the distance using the period-luminosity relations. We also estimated the mass loss rate using the calibration relations between mass loss rate and K - [12] index. From the position in infrared color-color diagrams, we confirmed the photometric classification of KP2001-221 as a semiregular variable, based on the light curve of the NSVS database. For the N-type carbon star KP2001-77 we estimated distance and absolute magnitude M K using different calibration methods. For the remaining four objects we derived the absolute magnitudes and distances using our CCD spectra and published JHK S magnitudes. We discuss the nature of these objects on the basis of the obtained results.

The spotting activity of the dwarf system CM Dra (dM4.5+dM4.5) is analyzed using new photometric observations taken in the spring of 2005 using the multichannel photometer and 70-cm telescope at the Astronomical Observatory of the Urals State University. A light curve constructed for this system revealed a rotational brightness modulation of low amplitude, 0m.016, owing to cold spots analogous to those on the sun. The longitude of maximum spotting is found to be 263°±4° perpendicular to the line between the centers of the components. A comparison with our earlier observations in 1996-1997, as well as with published data, shows that during different epochs a spotting maximum is observed in the hemisphere of the principal component which faces the secondary component and is shifted by 30° relative to the line between the centers along the direction of rotation of the star. This may indicate a role for tidal effects in creating the magnetic activity of CM Dra. Grouping of flares in time is observed, even for long-term observations. This appears to be related to the passage of large active regions across the star’s disk and may indicate a possible cyclical activity of CM Dra.

The results of optical R-band photometry of three X-ray selected BL Lacertae objects 1ES 0502+675, 1ES 0806+524 and 1ES 1959+650 from the Einstein Slew Survey are presented. The observations are performed during 1997–2006 with the 70-cm meniscus type telescope of Abastumani Astrophysical Observatory. The objects show clear long-term variability with time scales of 1–3 years without evident periodicity. The main results consist in the discovery of multiple-peak structures on historical light curves as predicted theoretically on the basis of the assumption that long-term variability of blazars are triggered by ultrarelativistic shock waves propagating through their jets. They are direct evidence of the existence of reverse shocks besides the main one arising by a single disturbance. Two-peak maxima are found for 1ES 0502+675 and 1ES 0806+524. The more complicated structure shows 1ES 199+650 - a maximum with four consequent peaks. The relative strengths of the main and reverse shocks are mainly equal according to the shape of the respective peaks. The brightness dip between them is on average 60% less than in the case of consequent main shocks. Optical maximum epochs, covered well by the observations, show that the main shocks are either not always accompanied by reverse ones or the later are not always strong enough to be discovered by the observations.

This is a study of photometric data from the Hipparcos catalog and spectrophotometric observations by a group of Pulkovo observers in Bolivia of the variable star 2 Cen (V806 Cen). Fourier analysis yields a more precise value of 12.57 d for the period of the brightness variation instead of 12.0 d. Light curves constructed from the photometric data are found to have a smooth systematic variation with an amplitude on the order of 0m.2. Short duration changes in the brightness by 0m.1 take place over times of a few hours. The differences in the temperature and radius of the emitting layer at maximum and minimum brightness, which occur at phases of 0.00 and 0.58, respectively, are found. At the maximum the radius was smaller by 6% and the temperature was higher by 70 K; these differences may characterize the star’s pulsations.

Radical readjustments in the photometric activity of young stars owing to sudden changes in the circumstellar extinction are discussed using the light curves of two UX Ori type stars, CQ Tau and V1184 Tau, as examples. Changes of this sort can be caused by large deviations from axial symmetry in the distribution of circumstellar dust, as well as by large variations in the mass accretion rate in circumstellar disks. A large amount of dust may also appear in the vicinity of a young star owing to collisions of planetesimals.

Results from two-color VR photometry of the unique cataclysmic magnetic variable star V1432 Aql and a theoretical model of these data are presented. The accuracy is improved by using the “mean-weighted comparison star” method. The derivative of the rotational period is dP/dt = −1.11(±0.016)·10−8. The characteristic synchronization time for the rotational and orbital motions of the white dwarf is 96.7±1.5 years, in good agreement with theory for the acceleration of an asynchronous propeller owing to the angular momentum of accreting matter. A third type of minimum detected in the light curve is interpreted in terms of the presence of an arc, or ring, rather than an accretion disk. A theoretical model is developed for determining the capture radius of accreted matter by the magnetic field of the white dwarf using the phase difference between the two types of minima associated with the axial rotation. This parameter is estimated to be 16–28 times the radius of the white dwarf for an inclined column model. A dependence of the main characteristics of the system on the mass of the white dwarf is derived which yields better values for the range of this quantity than those determined by indirect methods. For the assumed masses (M1 = 0.9 M⊙ and M2 = 0.3 M⊙) the estimated accretion rate is ∼7×10−10 M⊙. It is shown that in a synchronizing polar the contribution to the change in the period by the variation in the angular momentum of the white dwarf is negligible compared to the accretion torque. In the future multicolor monitoring is needed for studying the spin-orbital synchronization and periodic changes in the accretion structure caused by “spinning” of the white dwarf.

The properties of such phenomena as the appearance of humps at the ascending branch or double peaks in the light curve of long-period pulsating stars are examined. The characteristics of humps and the average light curves are obtained for a group of Mira-type stars and semiregular (SRa) variable stars. Correlations between the parameters of the light curves and the characteristics of the humps for these stars are discussed. The results obtained here are compared with published theoretical models.

The stars e Aur, KH 15D, and H 187 are utterly different in their fundamental characteristics. However, they share two important features: (1) prolonged eclipses are observed in all three and (2) there are no spectroscopic signs of a second component. The light curves of these objects are substantially similar, which may indicate a uniform mechanism for the eclipses. This article analyzes models for eclipsing in these objects proposed by different authors and discusses the problems associated with their application.

Results are presented from an analysis of observations in a sample of 53 long-period pulsating stars (44 of which are Mira-type and 9 are semiregular variables). A catalog of the characteristics of the individual pulsation cycles of the light curves is obtained for these stars. A correlation analysis of the characteristics of the individual pulsation cycles is carried out for each star. A number if diagrams relating the variability of the characteristics of the individual cycles to the average parameters of the variability of the stars and to their spectral classes. New criteria for classifying long-period variables are proposed on the basis of these diagrams.

The hypothesis that W Cep has an eclipsing variability is discussed on the basis of our photometric and polarimetric observations of it from 1983–2003. Here we attempt to use our observations of W Cep to construct an average light curve, after separating out the slow variation, with the elements JDmin=2448105d+2090d. A strong variability is found from period to period at phases of 0.1–0.3 that may be caused by a variable flow of matter between the components.

Data from the Pulkovo spectrophotometric data base on the absolute quasimonochromatic fluxes from oCet in the 320–1080 nm range are used to determine the physical parameters of this star in different phases of its light curve. The continuum emission layer is found to expand between the phases of the cycle corresponding to the rising and falling branches of the light curve. The average expansion velocity is 32 km/s. By the time the star’s brightness has fallen by roughly three magnitudes, its radius has increased by almost a factor of three. Over this same time the temperature of the layer has fallen from 3000 K to 2200 K. For this expansion velocity, the calculated mass rate loss is ⊙ M /year.