We analyzed RXTE data from the burst of the year 2000 of the X-ray millisecond binary pulsar SAX J 1808.4-3658 with the intent of determining the new orbital parameters.

We used the observations of SAX J1808.4-3658 performed by the Rossi X-Ray Timing Explorer (RXTE) when the source was again detected in outburst during the period January-March 2000 (Wijnands et al. 2001). In particular we examined the data from the Proportional Counter Array (РСA) (Jahoda et al. 1996). We first applied barycentric correction to the data using the optical coordinates of the source (Roche et al. 98).

We present the results of optical and infrared photometry of the quiescent X-ray transient V404 Cyg during the period 1992-2003.

It is largely known that the Soft X-ray Transient (SXT) V404 Cyg exhibits short-term (sub-orbital) variations during quiescence (see eg. Pavlenko et al. 1996). It seems that fast variability during quiescence is not a peculiarity of V404 Cyg but a fingerprint of quiescent SXTs, irrespective of the nature of the compact object (Zurita, Casares & Shahbaz, 2003). Although these variations seem to originate in the accretion disc, the underlaying physical mechanism is not yet understood. Since V404 Cyg is the brightest SXT, and hence accessible with 1-m type telescopes, we embarked on a study of the fast variability over the period 1992-2003.

During two observational seasons of international campaign of YY Her we secured photometric data which covered the primary as well as the secondary minima and revealed unexpected outburst activity of this system.

YY Her belongs to the classical symbiotic binaries with nova-like outbursts. Recently Mikolajewska et al. (2002) explained the light variability of YY Her by combining the ellipsoidal changes and sinusoidal variations of the nebular continuum and line emission. In 2001 (Hric et al. 2001) we discovered in the binary system YY Her the presence of the secondary minimum that was indicated, however, by only three photometric observations from one observatory.

Some aspects of the recent activity period of the peculiar symbiotic binary CH Cyg, which has ejected both bipolar jets and discrete centrifugal outflows, are discussed.

In symbiotic binaries, the red giant's wind is accreted onto the white dwarf. High luminosity of the hot components (Lhot ~103L⊙, reaching ~104L⊙ in the outbursts) (Mikołajewska 2003; Sokoloski 2003) indicates that the accreted matter undergoes thermonuclear burning. There are about 10 symbiotic stars which have ejected high-velocity, collimated, bipolar jets. Some of them show flickering of the optical light on the time scale of minutes. Both jet ejection and flickering indicate that an accretion disk should be present in those systems. Jet emitting symbiotic stars seem to have lower luminosity of the hot component ( ~1 – 100 L⊙) than in most other symbiotics.

Analysis of the optical and infrared photometry together with UV spectroscopy led to discovery of the 15-years periodicity in the symbiotic system V1016 Cyg. This period could be interpreted as a orbital period in the binary system consisting of the Mira variable and the hot white dwarf.

We have analyzed long-term optical photographic and UBV photoelectric photometry of V1016 Cyg. Collected observations cover pre- and post-outburst stages of the system. The light, curve suggests four stages of activity: the pre-out burst flare in 1949, the main nova-like outburst in 1904, and two post-outbursts, decreasing-amplitude flares in 1980 and 1994, respectively. Activity episodes affecting the system repeat with an interval of ~ 15 years. The ephemeris for the activity maxima is (see Parimucha et al., 2000).

By use of ground based IR photometry, we have studied the dust obscuration events of the symbiotic nova RR Tel which is a binary composed of a cool mira and a hot white dwarf. The JHKL light curves were corrected for Mira pulsations and correlated to the AAVSO visual light curve. We compare the behaviour of the three obscurations in different wavelength bands and propose interpretations of the results.

Planetary nebulae (PNe) represent a well defined stage of stellar evolution, where the characteristics of both, the central star and the gaseous envelope have defined properties. A large fraction of PNe contain binary nuclei, therefore, binary evolution plays an important role in the AGB and proto-planetary stages under certain circumstances. Symbiotic nebulae with extended envelopes (D-type), are identified with binary systems where the primary component is usually a Mira giant and the companion a hot white dwarf. Some of these systems resemble planetary nebulae and as a consequence can lead to misleading interpretations. Here we discuss some relevant links and differences between these two types of nebulae.

We have developed a new code for the calculation of synthetic spectra and vertical structures of accretion disks in cataclysmic variables and compact X-ray binaries. Here we present results for the CV system AM CVn.

AM CVn stars are a special type of cataclysmic variables, also called helium cataclysmics. They are systems of interacting binary white dwarfs, consisting of a degenerate C-O white dwarf primary and a low mass semi-degenerate secondary. The secondary loses mass, almost, pure helium, to the primary, forming an accretion disk. They have all in common a helium-rich composition, analoguous to the hydrogen-rich cataclysmic variables. They show photometric variabilities on time scales of ~ 1000s, the prototype of the class, AM CVn, e.g. exhibits a variability of ~ 18 min (Nelemans et al. 2001).

I have investigated the effects of including a more realistic cooling law in SPH simulations of accretion discs. In order to improve the efficiency of the simulations, I have used Strang operator splitting, and I have developed a method of timestep control which guarantees the accuracy and stability of the simulations.

Strang splitting (Strang, 1968) is used to numerically solve a differential equation where the differential operator is split into two or more parts. This scheme is appropriate for any such equation, but is applied most effectively in cases where one part of the equation has a different timescale to the rest, or is somehow more difficult to solve or less stable.

We investigate the accretion flow around the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from simulations by Okazaki et al. (2002) and Okazaki & Hayasaki (2004) for both a coplanar system and a misaligned system in which the Bo-star disk is inclined from the binary orbital plane by 30 degrees, with a short period (Porb = 24.3 days) and moderate eccentricity (e = 0.34). We find that a non-steady accretion disk is formed around the neutron star in the misaligned case as well as in the coplanar case. The disk size in the misaligned system is significantly larger because of its higher angular momentum than that in the coplanar system. We also find that the disk also evolves via a two-stage process, which consists of the initial developing stage and the latar developed stage.

We present rotating progenitor models for the WR+O binary systems HD186943 and HD90657 (van der Hucht, 2001) calculated with the evolutionary code described by Wellstein (2001). Due to rotation, the effective accretion onto the secondary star is reduced as it is spun-up close to its break-up velocity and thereby undergoes strong mass loss. We investigate the progenitor evolution of the two observed WR+O binary systems through stable mass transfer. We conclude that these systems evolved through Case A mass transfer as they have short orbital periods now (8…10 days), and the progenitor systems must have started with a shorter or equal period. We show that there has to be a significant mass loss from the binary system to produce WR+O systems similar to the observed ones. The accretion efficiency of the secondary star in our rotating models is ~10%. We compare properties of the observed and modelled systems in Table 1.

We spectroscopically observed WZ SGE in 11 nights during the 2001 superoutburst. The feature of the spectra dramatically varied from at the outburst maximum through during the rebrightening phase.

WZ SGE is the prototypical star of WZ SGE-type stars, a small class of SU UMa-type dwarf novae. WZ SGE stars have unusual characteristics of quite large outburst amplitudes up to ~8 mag, extraordinary long recurrence cycles of the outbursts (≥10 years), no (or only a few) normal outbursts.

We propose a new interpretation for the low radial velocity of He II emission line in the Galactic supersoft X-ray source RX J0019.8+2156 based on a 2-D numerical simulation of dynamical mass transfer in binary systems. A more massive main-sequence (MS) companion of ~ 2.0 M⊙ is derived for a ~ 0.6 M⊙ white dwarf (WD) primary.

The Galactic supersoft X-ray source RX J0019.8+2156 (hereafter, RX J0019) with a 12.2 mag optical counterpart was discovered by ROSAT. The source is a binary with the period of 0.66 days and its X-ray luminosity is fairly constant, at least, for 7 yrs. Therefore RX J0019 seems to be a typical luminous supersoft X-ray source (SSS) with steady hydrogen shell-burning on a mass-accreting white dwarf (WD).

We present R-band CCD photometry of the eclipsing dwarf-nova WZ Sge from six epochs after its 2001 outburst, using the 1.2m telescope of the NOA in Greece.

The big scatter of data on the light curve of T CRB is identified with the flickering activity of the system. The data performed during April 1996 have a falling trend and they can be a part of a downward branch of a long-term and energetically powerful flare. Estimated energy 2 1035 J and the duration of this event were compared with the theoretical assumptions based on three typical physical scenarios, which can be the source of flickering. The dissipation of magnetic loops and the existence of the turbulent eddies are energetically deficient, but these scenarios are real in the case of less powerfull flares. The real explanation could be the instability of the secondary and variable mass transfer rate through the Lagrangian point, therefore through whole disc.

Analysis of CCD photometry performed during 12 nights and the estimate of the distance based on the light curve is presented. The photometric data is modulated with a period of 3.7 h, which we interpret as the orbital period above the period gap distribution of cataclysmic variables. The VSNET light curve combined with data from IAU Circulars suggests a distance of 4.5±0.4 kpc based on t2/t3 time estimates. Two spectra 11 days after the maximum were taken. The expansion velocity of the envelope was derived to be 1658±62 km s–1.

A time-resolved optical spectroscopic study of the long-period (P=10.08h) old nova Q Cyg has revealed persistent yet erratic absorption features indicating the presence of a wind, while the system was rising to one of its stunded outbursts. Data taken with the WIYN 3.5m telescope show P Cygni profiles in the He I triplet lines at 5876Å and 7065Å, which are absent in the He I singlet emission line at 6678Å, despite the fact that the relevant energy levels of those three lines are at very similar excitation levels. The Hα line often has a red ward emission tail, characteristic of a receding outflow, and it possess a blueward absorption profile during only one wind event. Kafka et al. (2003) argued that this behavior is due to the strongly metastable 2 3S effective ground state of the He I triplets, which becomes over-populated in conditions of low density and a dilute radiation field, over-populating in turn the 23P common lower level of He I 5876Å and 7065Å, leading to absorption from a low density wind. Therefore, the triplet/singlet lines trace two different parts of the system: the wind and the disk respectively.

Photometric variability in cataclysmic variables (CVs) on time scales longer than a few days can be most effectively addressed by automated long-term monitoring programs such as that of RoboScope (Honeycutt & Turner 1992): more than 100 CVs have been monitored for about 13 years, obtaining 75 to 150 measurements per year for each system. Among the techniques being explored for analysing this data set is the use of the structure function (SF), an autocorrelation tool employed extensively for the study of the light curves of AGNs (e.g. Hufnagel & Bregman 1992). A first order SF measures the scatter in a time series of magnitudes, m, as as a function of the time lag, τ (Hughes, Aller & Aller 1992).

GG Carinae is a peculiar emission line object classified as a B[e] star. Using high resolution data we confirm that GG Carinae is at same time a binary system and a variable star.

GG Carinae was classified by Lamers et al. (1998) as a B[e] star and also is pointed out as a binary system. So, any investigation to determine its parameters requires an detailed analysis in order to know and to separate the effects of each component. Gosset et al. (1984) used Fourrier Analysis in the data obtained from photoeletric photometry of both the standard UBV and Strongren system and calculated a period of 31D.02.

A spatially complete Hα survey of M81 for novae was conducted continuously over a 5 month interval using the Calypso Telescope at Kitt Peak, AZ. A raw nova rate for M81 gives 23 yr–1 which is a lower limit. Monte Carlo simulations using nova light curves and survey frame limits yield a nova rate of . Using this value and the K-band photometry for M81 from the 2MASS Large Galaxy Atlas of Jarret et al. (2003) gives a luminosity specific nova rate of .The spatial distribution of the novae follows the bulge light much better than the disk or total light according to KS tests of their radial distribution. The asymmetric nova distribution across the major axis line of M81 implies a bulge-to-disk nova ratio of > 9 and supports the idea that novae originate primarily in older stellar populations.