The outburst and eclipse characteristics of the eclipsing dwarf nova EX Dra prompted us to monitor it during the months July-August 2000 with the 1.2m telescope of the National Observatory of Athens (NOA). Here, we present an eclipse mapping study of the July 2000 light curves. B-band of the August 2000 data have been presented by Harlaftis et al. (2002).

We present and discuss the Scargle periodograms of fast-speed B-band optical photometry of the eclipsing dwarf nova EX Draconis during quiescence and outburst, obtained with the 1.2m telescope of the National Observatory of Athens (NOA) in July 2000. We report on the discovery of a 143 s periodicity which most likely is related to the spin period of the white dwarf. We also find periodicities near 115 and 123 seconds during outburst which may be caused by pulsations of the accreting white dwarf in response to the enhanced mass transfer rate.

New CCD observations of the pulsating star SZ Lyn are analyzed and a new ephemeris is proposed. The photometric data collected over the last 43 years are used to determine and update the pulsational and orbital elements, based on the light-time effect detected in the O-C diagram.

We report multicolour photometric observations of the 2003 eclipse of the long-period (5.6 yr) eclipsing binary EE Cep. Measurements were obtained with ten telescopes at eight observatories in four countries. In most cases, UBV(RI)C broad band filters have been used. The light curve shape shows that the obscuring body is an almost dark disk around a low-luminosity central object. However, variations of the colour indices during the eclipse indicate that the obscuring body emits a considerable amount of radiation in the near infrared.

New ground-based BV RI CCD observations of the eclipsing binary systems NN Vir and YY CrB are analyzed and illustrated. New times of minima are given and new ephemerides are proposed. The light curves are analyzed with the Wilson-Devinney light curve synthesis code and new geometric and photometric elements are derived. These elements are used together with the available spectroscopic data to compute absolute elements. The evolutionary status of each system is studied by means of mass-radius diagrams. The systems NN Vir and YY CrB are found to be A-type and W-type W UMa systems, respectively.

The paper presents new geometric, photometric and absolute parameters, derived from combined spectroscopic and photometric solutions, for ten contact binary systems. The analysis shows that three systems (EF Boo, GM Dra and SW Lac) are of W-type with shallow to moderate contact. Seven systems (V417 Aql, AH Aur, YY CrB, UX Eri, DZ Psc, GR Vir and NN Vir) are of A-type in a deep contact configuration. For six systems (V417 Aql, YY CrB, GM Dra, UX Eri, SW Lac and GR Vir) a spot model is introduced to explain the O'Connell effect in their light curves. The photometric and geometric elements of the systems are combined with the spectroscopic data taken at David Dunlap Observatory to yield the absolute parameters of the components.

The physical parameters of ten eclipsing binaries (eight contact and two semi-detached) are derived by using ground-based photometric observations and Hipparcos/Tycho photometric data, which mimic the photometric observations that are expected to be obtained by Gaia. The results are compared and the achievable precision of the basic stellar parameters derived by Gaia photometry is discussed.

New BVRI light curves of the eclipsing binary system V1363 Ori, based on CCD observations made at the University of Athens Observatory, are analyzed using the Wilson-Devinney light curve synthesis code and new geometric and photometric elements are derived. These elements are used together with the available spectroscopic data to compute the absolute elements of the system. The evolutionary status of the system is also discussed.

The nova-like variable TT Ari had shown a luminosity change with a drastic change of the light curve. This state is distincly different from both the bright "negative superhump" state and the "positive superhump" state known before.

The double-mode pulsation of GSC 00144-03031 has been detected when searching for COROT targets. A very large dataset composed of 4722 photometric measurements was collected at six observatories in Europe and America. There is no hint of the excitation of additional modes (down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a pure double-mode pulsator, with a very short fundamental radial mode (P = 84 min). From uvbyβ photometry and evolutionary tracks it appears to be a Pop. I star with M = 1.75 M⊙, located in the middle of the instability strip, close to the Zero-Age Main Sequence. We also discovered other new double-mode pulsators in the databases of large-scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3, ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observational Petersen diagram is presented and explained by means of new models. A common sequence connecting Pop. I stars from the shortest to the longest periods is proposed and the spreads in the period ratios are ascribed to different metallicities (at the shortest periods) and to different masses (at the longest ones).