P. Rovithis

A photometric study of the W UMa-type system U Pegasi

In the present study, the activity of the eclipsing binary of the W UMa-type system U Peg is examined by analysing the photoelectric observations covering the period from 1950 to 1989. During this period, the light curves show signicant dierences and asymmetries. The analysis of the corresponding light curves is made using Djura sevi cs inverse problem method. To explain the light-curve asymmetries and variations, we used a Roche model that involved regions containing spots on the components. The analysis shows that the system U Peg is in an overcontact conguration (f over 14:9%). The Roche model with spotted areas on the cooler component yields a good t of the observations for the whole set of the analysed light curves without any changes of the basic system parameters. This indicates that the complex nature of the light-curve variations during the examined period can be explained by the evolution and motion of spotted areas on the cooler component. According to the obtained results, the spotted areas cover a signicant part of the stellar surface; the changes in their location and size with time are examined.

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.

A photometric study of V566 ophiuchi

The A-type W UMa system V566 Oph was observed photoelectrically in two wavebands (B andV) in the years 1988-1989 at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece. The light curves of the system are analyzed using frequency-domain techniques and new geometric and photometric elements are derived. These elements are combined with the more recent spectroscopic data based on Reticon observations to yield the absolute parameters of the system. The evolutionary status of the system is considered and it is found that V566 Oph has started its evolution away from the Main Sequence. The period of the system continues to increase.

Photoelectric observations of BV Draconis

In this paper the twoB andV light curves of the close eclipsing binaryBV Draconis, obtained with the 48-in reflector of the National Observatory of Athens, are represented and discussed. Also, new period of the system is given.

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.

The system of DO cassiopeiae: Photoelectric observations and light curves analysis

The newB andV photoelectric observations of DO Cas, obtained during 1979 and 1980, are presented, analysed, and discussed. The observations were made at the National Observatory of Athens, Greece, and their analysis was based on the frequency domain, techniques. New geometric, photometric, and absolute elements for the system are given.

The electron temperatures of NGC 2024 and IC 434

In this letter new results about the electron temperaturesTe of the NGC 2024 and IC 434 are given. They were found by the method of the ratioBHx/B[N u] (Baudel, 1970). Accepting for the exciting stars the spectral types given by Georgelin (1969) our results were found to be in good agreement with Hjellmings (1968) theoretical predictions.