A sequence of V-band light curves of the active close binary RT Lacertae (G5+G9 IV), extending from 1965 to 2000, is presented and analysed to derive the spot distribution and evolution on the component stars. In our modelling approach, the Roche geometry and Kurucz's atmospheric models were adopted. The resulting maps of the spot surface distribution were regularized by means of the Maximum Entropy and Tikhonov criteria to take full advantage of the increased geometrical resolution during eclipses. By comparing the maps obtained with these two criteria, it was possible to discriminate between surface features actually required by the data and artifacts introduced by the regularization process. Satisfactory fits were obtained assuming spots on both components and the unspotted V-band luminosity ratio: L-G5/L-G9 IV = 0.65+/-0.05. The more massive G5 primary appears to be the most active star in the system and its spotted areas are mainly responsible for the light curve distortions. The yearly spot distributions on both components indicate that their spot patterns consist of two components, one uniformly and the other non-uniformly distributed in longitude, the latter suggesting the presence of preferential longitudes. In particular, spots are concentrated around the substellar points and their antipodes on both stars. The eclipse scanning reveals spots with diameters of similar to40degrees, or possibly smaller, on the hemisphere of the primary star being occulted. The primary shows clear evidence for a short-term activity cycle with a period of similar to8.5 yr and a possible long-term cycle with a period of approximately 35 yr. The variation of the spot migration rate may be related with surface differential rotation, with a lower limit of DeltaOmega/Omega similar to 3.2x10(3). The G9 IV secondary does not show evidence for an activity cycle, its spot coverage appearing rather constant at similar to15-20% of its surface. The relative amplitude of its surface differential rotation, as indicated by the variation of the spot migration rate, is DeltaOmega/Omega similar to 2.7x10(3). The variation of the orbital period shows a correlation with the activity level of the primary component. Specifically, the decreases of the orbital period appear to be associated with minimum spottedness and sizeable changes of the surface spot distribution that may be related to increases of the rotation rate of the spot pattern. Conversely, an episode of increase of the orbital period was related to an increase of the spotted area on the primary star. Such results support the recently proposed models that connect the perturbations of the orbital dynamics with the variation of the figure of equilibrium of the active components, due to the operation of non-linear hydromagnetic dynamos in their extended convective envelopes.

The light curves of the chromospherically active eclipsing binary RT Lacertae obtained from 1993 to 1999 are analyzed here. The variation of the brightness at mid-eclipses and at maxima is carefully re-examined. The largest variation was obtained at mid-primary, where the more massive, hotter component occults the less massive cooler secondary star. Therefore, we suggest that the variation of the system's brightness mainly arises from the more massive star. The mean brightness of the system indicates a cyclic change. It showed at least two jumps during the last 22 years. The first occurred in 1984 and the second in 1994. Therefore, the length of the magnetic cycle appears to be about ten years. All the timings of the mid-eclipses obtained so far were collected and analyzed under the assumption of the third body hypothesis. A period of 94 yr was found for the third body orbit. The variation of the systemic velocity of the eclipsing pair seems to confirm this suggestion. The time delay and advance due to the orbit of the eclipsing pair around the third component were computed and subtracted from the original residuals obtained with the linear light elements. The remaining residuals also show a quasi-periodic change. The period of this change was calculated to be about 18 yr. This second O-C change may be related to the magnetic activity of the more massive component.

Eclipsing binary system DI Her has an apsidal motion and its observed apsidal advance seems to be less than even the relativistic advance. Therefore many debates are centered about DI Her, which may also be extended to more or less similar systems showing such a discrepancy between the theory and the observations. Computed value of the apsidal motion rate from the eclipse timings of DI Her, up to now, is very small and about one fourth of the relativistic advance. In this work we show that such a small observed rate is due to use of visual and photographic data having low precision, and due to disregarding the large orbital eccentricity of the system. As a result, we found that the observed apsidal advance is still less than the relativistic advance, but is larger than the previous results by a factor of about two.

New photometric data from the eclipsing binary star AI Draconis has been analyzed with the method of Wilson-Devinney. The system shows a period increase of about 0.91 sec per century, which corresponds to amass transfer from the less to the more massive component at a rate of 7.5 10(-7) M./yr under the conservative mass transfer hypothesis. We also suggest that the system has an unseen component which orbits around the mass center of the triplet system with a period of about 23 yrs. We found that the projectional angular separation between the third star and eclipsing pair varies from 0." 048 to 0." 235. These results suggestive of a third body should be checked in the future with more sensitive observations.

We present the main results of a photometric and spectroscopic study of the lambda Boo star 29 Cyg carried out from 1995 - 1998.

New UBVR light curves of the eclipsing binary HTN Vir have been obtained. All the published times of primary and secondary eclipses have been collected. By adding the new times of the eclipses obtained by us; the general behavior of the O-C changes has been revealed. The updated O-C change seems to show a cyclic character. This behavior may be the result of whether rotation of the apsis connecting the star's centers or revolution of the couple around a third body. The former has been excluded due to the fact that the O-C values of primary and secondary eclipses show similar variation, i.e., not 180 degrees out of phase. Therefore the O-C changes have been analysed under the assumption of the light-time effect. The period of revolution around the third body was found to be 19 years. The time span following the discovery of eclipsing nature of the system covers 69 percent of the period predicted. The B, V and R light curves have been analysed by the WD code and the physical parameters of the components were obtained. The hotter, primary component is an sdB star with a temperature of about 36 000 K, and the cooler one is a late-type main sequence star with a temperature of 3300 K. The physical parameters derived for the secondary component are in accordance with the parameters of the theoretical models. This analysis indicates that the low mass, cooler secondary does not fill its critical Roche lobe. Therefore, mass accretion from the cool main sequence star to the hot sdB primary is not yet expected.

The preliminary results of a 1996 multisite campaign on the pulsating lambda Bootis star 29 Cyg are presented. This campaign, initiated by the Central Asian Network (CAN), allowed to collect data during 48 photometric and 2 spectroscopic nights at observatories of Ukraine, Kazakhstan, Turkey, Hungary, Canada and USA. The multiplicity of excited modes is confirmed in both spectroscopy and photometry. The analysis of all 1995 and 1996 data, combined with new CAN observations made in July-October 1997, is under way.

The light curves, obtained by the authors of the present paper during the period 1978–1992, of the chromospherically active binary system RT Lac were examined. The average (B–V) colour indices were obtained and corrected for the interstellar extinction. Spectroscopic studies indicate that the less massive component may be taken as G8. The light curve analysis indicates that the less massive, larger component fills its corresponding Roche lobe. Both photometric and spectroscopic observations compel one to draw a conclusion that circumstellar matter does exist around the binary system. A colour excess caused by this matter is found to be 0.278 for B–V colour at mid–secondary eclipse. On the basis of photometric colour indices alone, the components of RT Lac are classified as G3–4 and G8. If we use the observed radial velocities of the less massive subgiant star from Ca II emission lines and from other optical lines we find for the mass of the more massive component as 1.34–1.70 M ⊙ . This mass range corresponds to the main sequence late F stars. The common envelope hypothesis and mass function and also blending of the spectral lines of more massive component point out that it should be at most a late F type main sequence star.