Evolutionary state of W UMa-type systems

The evolutionary status of a sample of 31 W UMa-type systems (20 of W, 9 of A, and 2 of A/W sub-class) is examined and discussed on the basis of their positions in the H-R, mass-radius and mass-luminosity diagrams. The absolute elements of these systems have been evaluated by use of their spectroscopic and photometric data as they were found in the literature. Since different analysis methods have been used by the various investigators this gives the opportunity to make different H-R, mass-radius and mass-luminosity diagrams, according to the method used, and compare the results.Moreover, from the spectral type-period diagram of those systems that have spectral types from O to G2 it was found that all of them lie in the evolved region. Finally, the log (L _l/L _s) log (M _l/M _s) diagrams are presented and discussed.     

UV Leo: The Binary with the Two Suns

BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The elements of the two components of the system are calculated and the spot characteristics are given.     

Fourier analysis of the light curves of eclipsing variable stars

The aim of the present paper is to find the eclipse perturbations, in the frequency-domain, of close eclipsing systems exhibiting partial eclipses.After a brief introduction, in Section 2 we shall deal with the evaluation of thea _n ^(l) integrals for partial eclipses and give them in terms ofa ₀ ⁰ ,a ₀ ⁰ (of the associated -functions) and integrals; while Section 3 gives the eclipse perturbations arising from the tidal and rotational distortion of the two components. The are given for uniformly bright discs (h=1) as well as for linear and quadratic limb-darkening (h=2 and 3, respectively).Finally, Section 4 gives a brief discussion of the results and the way in which they can be applied to practical cases.     

Evaluation of the photometric perturbations in close binary systems

In the present study the photometric perturbations arising from the mututal tides of the two components in a close binary system are calculated and discussed. The evaluation is made for each star separately as well as for both stars together in the case of occulation eclipses terminating in totality.     

Evaluation of the photometric perturbations in close binary systems

In this study the photometric perturbations arising from the axial rotation of the two components in close binaries are calculated and discussed. The evaluation is made for occultation eclipses terminating in totality-for both stars together as well as for each component separately.     

Accretion disc in the massive V448 Cygni system

The UBV light curves of the early-type eclipsing binary V448 Cygni, obtained at the Abastumani Astrophysical Observatory from 1964 to 1967, are re-analysed here. The analysis was made assuming the presence of an accretion disc in the system, as inferred from the light-curve shape and spectroscopic characteristics of the system. The Roche model of a binary was used, containing a geometrically and optically thick accretion disc around the hotter and more massive star. By solving the inverse problem, the orbital elements and the physical parameters of the system components and of the accretion disc were estimated. This result is important for understanding the star formation and evolution processes in the systems with massive components.     

New photoelectric observations of VW Cephei

The aim of the present paper is to present the newB andV light curves of the eclipsing binary VW Cep, obtained with the 48-in. reflector of the National Observatory of Athens, Greece.In the introduction general information for the system is given. In Section 2 some observational and reductional details are given and the obtained light curves are represented. Section 3 deals with the period of the system which was found to continue its shortening. Finally, in Section 4, a general discussion concerning our light curves is given.     

The eclipsing binary BW Draconis

In this paper theB- andV-light curves of the eclipsing binary BW Draconis made at Kryonerion Station of the National Observatory of Athens during 1980 and 1981 are presented.     

The eclipsing binary AB Andromedae

In this paper the two newB- andV-light curves of the eclipsing variable star AB Andromedae, obtained during 1979 with the 48 in reflector of the National Observatory of Athens, are represented and discussed. General information of the system is given in the Introduction, while in Section 2 some observational and reductional details are given and the new light curves are represented. Section 3 deals with the period of the system and, finally, in Section 4 a general discussion is given.     

Ubvr light curves of 44i Bootis during 1978

In this paper theU, B, V, R light curves of the eclipsing variable 44i Boo, obtained during 1978, are represented and discussed.