Contact binaries are the most frequently observed type of eclipsing star system. They are small, cool, low-mass binaries belonging to a relatively old stellar population. They follow certain empirical relationships that closely connect a number of physical parameters with each other, largely because of constraints coming from the Roche geometry. As a result, contact binaries provide an excellent test of stellar evolution, specifically for stellar merger scenarios. Observing campaigns by many authors have led to the cataloging of thousands of contact binaries and enabled statistical studies of many of their properties. A large number of contact binaries have been found to exhibit extraordinary behavior, requiring follow-up observations to study their peculiarities in detail. For example, a doubly-eclipsing quadruple system consisting of a contact binary and a detached binary is a highly constrained system offering an excellent laboratory to test evolutionary theories for binaries. A new observing project was initiated at the University of Athens in 2012 in order to investigate the possible lower limit for the orbital period of binary systems before coalescence, prior to merging.

In the course of a photometric campaign undertaken at the University of Athens Observatory, the target 1SWASP J093010.78+533859.5 was observed and found to be a doubly-eclipsing quadruple system. This system was known as a contact binary since 2013, with an orbital period of 0.2277 days, and a detached binary lies along the same direction. Hipparcos astrometric observations confirm this finding, showing two stars with a common proper motion and an angular separation of only 1.7 arcsec. This favors the scenario of a true quadruple system, making 1SWASP J093010.78+533859.5 one of the very rare doubly-eclipsing quadruple systems known to date.

A model that contains a massive BH binary was proposed to explain the double peaked quasi-periodical (roughly about 12 years) outbursts of the blazar OJ287.

We present the results of a spectroscopic, photometric and orbital period variation analysis of the detached eclipsing binary V482 Per. We derived the absolute parameters of the system (M1 = 1.51 M⊙, M2 = 1.29 M⊙, R1 = 2.39 R⊙, R2 = 1.45 R⊙, L1 = 10.15 L⊙, L2 = 3.01 L⊙) for the first time in literature, based on an analysis of our own photometric and spectroscopic observations. We confirm the nature of the variations observed in the system's orbital period, suggested to be periodic by earlier works. A light time effect due to a physically bound, star-sized companion (M3 = 2.14 M⊙) on a highly eccentric (e = 0.83) orbit, seems to be the most likely cause. We argue that the companion can not be a single star but another binary instead. We calculated the evolutionary states of the system's components, and we found that the primary is slightly evolving after the main sequence, while the less massive secondary lies well inside it.

We present 110 times of minima of 23 eclipsing binaries.

We present results from the application of Kopal's method for eclipsing binaries to the analysis of the transit light curve of exoplanet HD 209458, using very accurate photometric observations made with the Hubble Space Telescope. The fitting of the model parameters to the data was achieved by use of the Simulated Annealing algorithm. Furthermore, we utilized a transformation of the limb darkening coefficients that negates the need to specify limits for their values (uninformative sampling), yet still yield physically plausible results.