Vassilios N. Manimanis

Period changes in six contact binaries: WZ And, V803 Aql, DF Hya, PY Lyr, FZ Ori, and AH Tau

Abstract Six contact binaries lacking a period analysis have been chosen to search for the presence of a third body. The O – C diagrams of these binaries were analyzed with the least-squares method by using all available times of minima. Ten new minima times, obtained from our observations, were included in the present research. The Light–Time Effect was adopted for the first time as the main cause for the detailed description of the long-term period changes. Third bodies were found with orbital periods from 49 up to 100 years, and eccentricities from 0.0 to 0.56 for the selected binaries. In one case (WZ And), a fourth-body LITE variation was also applied. The mass functions and the minimal masses of such bodies were also calculated and a possible angular separation and magnitude differences were discussed for a prospective interferometric discovery of these bodies.

The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class

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).

A photometric study of BH Cas

New CCD observations of the contact binary system BH Cas are presented in this paper. New times of minima and an ephemeris based on our observations are also given. Complete light curves obtained in the V , R and I lters have been analyzed with the Wilson-Devinney code to derive the geometrical and physical parameters of the system. The nal solution leads to a contact conguration (f 21 22%). We have found that the photometric mass ratio diers from the spectroscopic one by about 13%, a discrepancy which is not uncommon for other W UMa systems. The absolute elements of the system are used to study its evolutionary status. The results show that BH Cas is a fairly evolved W-type W UMa system.

Irregular amplitude variations and another abrupt period change in the

We report that the intermediate amplitude Scuti star V 1162 Ori has changed its main pulsational period in the course of the year 2000. This new period change falls in a sequence of period changes observed during the last 5 years. While the average amplitude value of all our new data, 63 mmag, ts a cyclic amplitude variation suggested by Arentoft et al. (2001), splitting the data up in smaller subsets discloses signicant deviations from regularity, with stretches of constant amplitude during short intervals of time. The new data show that the amplitude of one of the secondary frequencies, f2, has in 3 years dropped from more than 3 mmag to now about 1 mmag, and that the previously obtained f5 probably is a 1 d 1 alias of the real frequency. We present the newly

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The light curves of four eclipsing binaries (two near-contact and two contact) are analysed by means of light curve synthesis techniques to derive the geometric and photometric elements and the physical parameters of the systems. For the analysis we used ground based photometric observations and Hipparcos/Tycho photometric data, which mimic the photometric observations that should be obtained by GAIA, the approved Cornerstone 6 mission by ESA. The results are compared and the achievable precision of the basic stellar parameters derived by GAIA photometry is discussed.

Scuti star V 1162 Ori

The near-contact system RU UMi with an F0 primary and a K5 secondary was observed in U, B and V wavelengths in May and July 1998, as well as in March, May and July 1999. Six new observed times of minima are given and a new ephemeris is proposed. The basic parameters of the system extracted by our observations were used for spot modelling of the light curves. A simple spot distribution was determined, based on a model with one relatively small cool spot on the surface of the secondary. Absolute elements were calculated and the evolutionary status was determined. Our data favor a semi-detached conguration, with the secondary lling its inner Roche lobe; the primary must also be near the limits of its lobe.

On the performance of GAIA on photometry of eclipsing binaries: The case of four near-contact and contact systems

The near-contact system DM Del with an A2V primary and a G8 secondary was observed in U, B and V wavelengths in July 1998. A new seasonal light curve is presented and a new observed time of minimum is given. The unperturbed part of the light curve was used to determine some basic parameters of the system with the Wilson-Devinney code, some of which were kept fixed for spot modelling of the light curves. A simple spot distribution was determined, based on a model with two cool spots on the surface of the secondary. Absolute elements were calculated and the evolutionary status was determined.

A Photometric study of the near-contact system RU Ursae Minoris

The Russians became acquainted with the Christian religion in 860 A.D. In the middle of the 10th Century, Princess Olga of Kiev visited Constantinople and was baptized under the name Elene. Later, when her grandson Vladimir became a Christian, all the Russians became Christians too. Moreover, the Russians adopted the Cyrillic alphabet and the Julian calendar. In 1918 the government replaced the Julian calendar with the Gregorian one. However, the Russian Orthodox Church never accepted the Gregorian or the New Rectified Julian calendar. Even today it retains the old Julian calendar. An important but short-lived change in the history of the Russian calendar took place in the year 1929. Then the seven-day week was abolished being substituted with five-day intervals. This attempt was unsuccessful and finally the Soviet government restored the use of the initial Gregorian calendar and the ancient seven-day week.

UBV Photometric Study of the Eclipsing Binary DM Delphini

Rigas Velestinlis (Velestino 1757—Belgrade 1798), Greek national hero of fight against Turkish Empire and one of the forerunners of the Greek enlightenment movement, an important part of his life lived in Bucharest and tragically died in Belgrade, so that he is important and for Romanian and Serbian history. For the history of astronomy, interesting is his Anthology of Physics, where astronomical contents are present. In this contribution, his life and work are presented and analyzed, with a particular attention to the astronomical aspects of the mentioned work and his connections with Romania.

THE RUSSIAN CALENDARS AFTER THE CHRISTIANIZATION OF THE COUNTRY

We report on the results of a series of photometric observations of the low‐amplitude δ Scuti star GSC 4778:0324, in the course of a multi‐site campaign aiming at monitoring V1162 Ori. The two dominant frequencies, found in the previous analyses based on the 2000–2002 data, are confirmed and their amplitudes are found to be stable on a time‐scale of a few years.