Abstract. Light curves and photometric solutions of the contact binary XY Leo are presented. The UBVR light curves appear to be almost symmetric. The B and V light curves were analysed with the Wilson-Devinney code and the orbital parameters of the system were obtained and compared with those obtained in previous studies. All the times of minimum light were collected and combined with the new ones obtained in this study. The orbital period of the system oscillates with a period of 19.6 years and a semi-amplitude of 0.023 day. This regular change was analysed under the assumption of the third body hypothesis. 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 parabolic change. Therefore, we assumed that the orbital period of the system changes with time due to at least two different causes. The parabolic change of the period may be attributed to either mass transfer from less massive component to the more massive one, or an additional component bounded to the double binary system with a longer period.

Abstract. New photometric data set of the early type contact binary V 382 Cyg have been analyzed with emphasis on determining the photometric mass ratio of the system. The result (q = 0.68) supports the value given by Popper & Hill (1991). A study of the system using new data shows a period increase of about 3.28 s per century, which corresponds to a very large rate ∼ 5.0 10 −6 M /yr of mass transfer from the less massive to the more massive component under the conservative mass transfer hypothesis.

We present a ground based photometry of the low-temperature contact binary BB Peg. We collected all times of mid-eclipses available in literature and combined them with those obtained in this study. Analyses of the data indicate a period increase of 3.0(1) × 10 −8 days/yr. This period increase of BB Peg can be interpreted in terms of the mass transfer 2.4×10 −8 M ⊙ yr −1 from the less massive to the more massive component. The physical parameters have been determined as M c = 1.42 M ⊙ , M h = 0.53 M ⊙ , R c = 1.29 R ⊙ , R h = 0.83 R ⊙ , L c = 1.86 L ⊙ , and L h = 0.94 L ⊙ through simultaneous solution of light and of the radial velocity curves. The orbital parameters of the third body, that orbits the contact system in an eccentric orbit, were obtained from the period variation analysis. The system is compared to the similar binaries in the Hertzsprung-Russell and Mass-Radius diagram.

Abstract. New light curves and available times of minima of a β Lyr system EG Cep were analysed to deduce more information on the nature of the system. The main U-shaped (O − C) variation was interpreted in terms of the mass transfer and mass loss in the system. The same variation was also considered as a part of a sinusoidal variation and thus interpreted in terms of a light-time effect due to an unseen component in the system. New B and V light curves were analyzed with different fitting procedures, and there is general agreement that both stars must be very close to each other and to stability limits. A model that fits all the data well has a near main sequence primary and a secondary star that is overflowing matter towards it. This secondary is also reasonably close to main sequence conditions. The configuration thus appears to be a (relatively uncommon) 'Case A' type evolving Algol and raises interesting questions about such interactive evolution and potentially useful tests of theory.

Binary systems showing both apsidal motion and light travel time (LTT) effects which cause orbital period changes in close binaries were studied. 15 triple systems showing apsidal motion were found by searching the literature, and a table including the important parameters of these systems was constructed. Six of the systems given in this table were selected and observed photometrically. Existence of both apsidal motion and LTT effects in all selected systems was investigated by means of the analysis of their eclipse times. The mean observed internal structure constants, log =k2,obs, and contributions to the apsidal motion from the theory of General Relativity and the third/fourth bodies were calculated. The masses of the third/fourth bodies and some characteristics of their orbits were also calculated.