L. Hric

Outburst activity of the symbiotic system AG Dra

AG Dra is a well known bright symbiotic binary with a white dwarf and a pulsating red giant. The long-term photometry monitoring and a new behaviour of the system are presented. The detailed period analysis of photometry as well as spectroscopy was carried out. In the system of AG Dra, two periods of variability are detected. The longer one around 550 days is related to the orbital motion, and the shorter one around 355 days is interpreted as pulsations of the red giant in our older paper. In addition the active stages change distinctively, but the outbursts are repeated with the periods from 359 to 375 days.

Spectral behaviour of the eclipsing binary TX UMa around primary minimum

Sixty-one blue spectrograms of TX UMa were obtained in the years 1969–1970, mainly in phases close to the primary minimum of the eclipsing system. The radial velocity curve displays clear rotational effect from which much higher than synchronous rotational velocity of the blue (B8V) component has been formally derived. However, this discrepancy is probably due to the presence of the tenous accretion disk around the primary. The disk is apparently fed by the intermittent mass transfer as indicated by the occasional changes of orbital period of the system. From all available radial velocity data an improved set of spectroscopic orbital elements is derived. The behaviour of the spectral lines in and out of the primary minimum is compared. Metallic lines of the cold (F7IV) secondary component are clearly seen exclusively in phases 0.988 to 0.012.

THE ECLIPSING CATACLYSMIC TRIPLE SYSTEM V471 TAU

The precataclysmic variable V471 Tau was monitored photoelectrically in U, B, V and R colours since 1994 during 21 nights at the Skalnate Pleso, Stara Lesna and Kryonerion Observatories. The new times of minima had been derived. They may suggest that the cause of the (O — C) curve may be more complicated than what would correspond to the light-time effect only. The next season 2002/2003 will be crucial for definite confirmation of the behaviour of the (O — C) diagram of V471 Tau.

The orbital modulation of the X-ray binary V Sagittae in the high and low states

Our analysis of the orbital modulation of V Sge, carried out in the intensity scale instead of the previously used magnitude scale, revealed that the full amplitude of the modulation remains almost constant as the intensity of the system rises from the low to the high state. The primary minimum remains very similar, as regards both its depth and width. The secondary minimum tends to slightly lag behind phase 0.5. The depth of the secondary minimum is subjected to the largest changes; it becomes almost as deep as the primary minimum during the high state while it is significantly more shallow than the primary one in the low state.

Orbital period change during the outburst of the symbiotic binary V 1329 Cygni

Photographic photometry of the symbiotic nova V 1329 Cygni performed at the Skalnaté Pleso Observatory in the years 1979–1991 is presented. An observational proof of the 11d.4 orbital period increase caused by the nova-like outburst around 1966 is given. New ephemeris valid after the year 1971 is as follows: JDmin = 2446784.862 + 963d.306 ×E. The arguments in favour of accretion powered outburst are given.

The new helium-weak star HR 446

The CP star HR 446 (HD 9531, B8p V,m=5.69) is one of the CP stars with no definitely assigned peculiarity type. In this contribution it is shown by application of the synthetic spectra, that the star is a helium-weak type of the titanium-strontium subgroup. Photometric observations confirmed the rotational period of 0.6684 d discovered earlier. Our photometric observations do not permit to find rapid variability exceeding 0.005 mag within the limits of 5–300 min.

Pulsation of IU Per from the Ground-based and ‘Integral’ Photometry

Abstract IU Per is an eclipsing semi-detached binary with a pulsating component. Using our own ground-based, as well as INTEGRAL satellite photometric observations in the B and V passbands, we derived geometrical and physical parameters of this system. We detected the short-term variations of IU Per in the residuals of brightness after the subtraction of synthetic light curves. Analysis of these residuals enabled us to characterize and localize the source of short-term variations as the pulsations of the primary component typical to δ Scuti-type stars.

Pre-Cataclysmic System V471 Tau with Confirmed Brown Dwarf and Suspected Extrasolar Planet

We can show that analysis of the (O-C) diagram is a powerful method of detecting new bodies in binary systems. For this purpose we need very symmetric minima with precisely determined shapes. In the case of good covering by observations with high time resolution, it is possible to determine the times of such minima with sufficient accuracy. In the case of V471 Tau, the (O-C) diagram gave us residua which can be explained by the presence of a fourth body with substellar mass in the system.

Hard X-ray and Optical Activity of Intermediate Polars

Intermediate polars represent a major fraction of all cataclysmic variables detected by INTEGRAL in hard X-rays. Nevertheless, only 25% of all known intermediate polars have been was detected in hard X-rays. This fact can be related to the activity state of these close interacting binaries. Multi-frequency (optical to X-ray) investigation of intermediate polars is essential to understand the physical mechanisms responsible for the observed activity of these objects.

The Problem of the Flickering Activity of the Recurrent Nova T CrB

On the basis of our previous paper (Hric et al. 1998) we can proclaim that the existence of two emission‐line regions can remarkably affect the flickering activity in the binary system. We could expect flickering activity dependence on the orbital phase. Deriving the energy of the flickering and comparing the derived value with the energy particularly needed for three possible areas where the source of the flickering could be settled down, we found the most plausible area to be in the unstable accretion onto the white dwarf, i.e. the boundary layer.