V. Keskin

Absolute Properties of the Binary System BB Pegasi

We present ground-based photometry of the low-temperature contact binary BB Peg. We collected all the times of mid-eclipse available in the literature and combined them with those obtained in this study. Analyses of the data indicate a period increase of × 10-8 days yr-1. This period increase of BB Peg can be interpreted in terms of the mass transfer 2.4 × 10-8 M⊙ yr-1 from the less massive to the more massive component. The physical parameters have been determined as Mc = 1.42 M⊙, Mh = 0.53 M⊙, Rc = 1.29 R⊙, Rh = 0.83 R⊙, Lc = 1.86 L⊙, and Lh = 0.94 L⊙ through simultaneous solutions of light and of the radial velocity curves. The orbital parameters of the third body, which orbits the contact system in an eccentric orbit, were obtained from the period variation analysis. The system is compared to the similar binaries in the Hertzsprung-Russell and mass-radius diagrams.

The short-period low-mass binary system CC Com revisited

In this study we determined precise orbital and physical parameters of the very short-period low-mass contact binary system CC Com. The parameters are obtained by analysis of new CCD data combined with archival spectroscopic data. The physical parameters of the cool and hot components are derived as Mc = 0.717(14) M� , M h = 0.378(8) M� , Rc = 0.708(12) R� , R h = 0.530(10) R� , Lc = 0.138(12) L� ,a ndL h = 0.085(7) L� , respectively, and the distance of the system is estimated as 64(4) pc. The times of minima obtained in this study and with those published before enable us to c

The new light curves and period study of AK Herculis

B andV observations of the W Ursae Majoris-type eclipsing variable system AK Her were made on five nights at the Ege University Observatory. Several times of minima were obtained during the observations and the new light elements were calculated. The light-time period was found to be about 75.72 years. The light curve of the system appears to change in each cycle for both colours. The secondary minimum of the system seems to be a total eclipse with a duration of about 42m.5.

Preliminary results of the alignment and Hartmann tests of the AZT-22 telescope

The AZT-22 telescope installed in Turkey (Antalia) was aligned and tested on stars by the Hartmann method. The rms normal deviation of an equivalent optical system is 0.040±0.016 µm. The circle of confusion is 0.40±0.04 arcsec in diameter at a 50% energy level.

Long-Term Photometry of RT Lacertae: 1. Light and Colour Variation

The peculiar chromospherically active binary system RT Lac was observed in B and V bands between 1989 and 1992. The four-year photoelectric B and V light curves are presented. The light and colour variations in the four special regions of the light curve between 1978 and 1992 are discussed. The available photometry obtained by the present authors defines at least three consecutive maxima in the variation of the brightness of the system at second maximum and in mid-primary eclipse. The behaviour of the light and colour changes in mid-primary and at second maximum harmonizes with the common property of the RS CVn-type binaries. However, the light changes at first maximum do not resemble either at second maximum or in mid-primary minimum. Therefore, we conclude that the observed features cannot be attributed to the spottedness of the more massive component alone. The signs of the starspots are masked by the matter in front of the more massive component at the first maximum. The present data indicate that the magnetic cycle in RT Lac is about 12 years, which is analogous to the Suns 11-year sunspot cycle.

Long–term Photometry of RT Lacertae: 2. Further Evidence fo a Circumstellar Envelope and MAss Accretion

The light curves, obtained by the authors of the present paper during the period 1978–1992, of the chromospherically active binary system RT Lac were examined. The average (B–V) colour indices were obtained and corrected for the interstellar extinction. Spectroscopic studies indicate that the less massive component may be taken as G8. The light curve analysis indicates that the less massive, larger component fills its corresponding Roche lobe. Both photometric and spectroscopic observations compel one to draw a conclusion that circumstellar matter does exist around the binary system. A colour excess caused by this matter is found to be 0.278 for B–V colour at mid–secondary eclipse. On the basis of photometric colour indices alone, the components of RT Lac are classified as G3–4 and G8. If we use the observed radial velocities of the less massive subgiant star from Ca II emission lines and from other optical lines we find for the mass of the more massive component as 1.34–1.70 M⊙. This mass range corresponds to the main sequence late F stars. The common envelope hypothesis and mass function and also blending of the spectral lines of more massive component point out that it should be at most a late F type main sequence star.

Close binary system GO Cyg

abstract In this study, we present long term photometric variations of the close binary system GO Cyg. Modellingof the system shows that the primary is filling Roche lobe and the secondary of the system is almost fill-ing its Roche lobe. The physical parameters of the system are M 1 = 3.0 ± 0.2M , M 2 = 1.3 ± 0.1M ,R 1 = 2.50 ± 0.12R , R 2 = 1.75 ± 0.09R , L 1 =64±9L , L 2 = 4.9 ± 0.7L , and a = 5.5 ± 0.3R . Our results showthat GO Cyg is the most massive system near contact binary (NCB). Analysis of times of the minima showsa sinusoidal variation with a period of 92.3 ± 0.5 yr due to a third body whose mass is less than 2.3M .Finally a period variation rate of 1.4 10 9 d/yr has been determined using all available light curves. 2011 Elsevier B.V. All rights reserved. 1. IntroductionStudies of the evolution of late-type close binary systems revealthat the evolution of detached, semi-detached and contact systemsare closely related (Yakut and Eggleton, 2005; Eggleton, 2010 andreference therein). The more massive star in a detached binary sys-tem fills its Roche lobe first because it has shorter evolutionarytimescale before its companion. The system is semi-detached bin-ary. In addition to nuclear evolution and mass loss, mass transferhas a crucial role in driving a binary towards a contact phase ofevolution. The observations of detached, contact and semi-de-tached binaries are crucial to our further understanding of the evo-lution of close binary systems.We therefore, include GO Cyg (HD 196628, GSC 02694-00550,V =8

Light variations and flares on V471 tauri

Two-colour photometric observations of the white-dwarf and K-dwarf eclipsing binary V471 Tau were made during the last four years. The resulting light curves and thirteen timings of mid-eclipse are presented. During the observations two flares were obtained on September 23 and December23, 1992. Both events occurred just after the fourth contact. The increment in the brightness was measured as 0.m067. The energy liberated by the flare was computed to be 5.43 × 1032 erg s−1 in the JohnsonB band, which amounts 1.13 times that of the total radiation of the K-dwarf.

Recent photoelectric photometry of the newly discovered eclipsing system BD + 13o4708

Two-colour photoelectric photometry of the eclipsing binary BD + 13o4708 was carried out. Several features such as asymmetry in the branches, light difference between the maxima, an eccentric orbit, a dip around phase 0.2 are distinctive. The new light elements of the system were computed using also the previous times of primary minima given by Walker (1988).

Light changes of the close binary system CN Andromedae

The photoelectricB andV colour observations of the β Lyrae-type eclipsing binary CN And were made on four nights at the Ege University Observatory. The new light elements, which were calculated by adding new times of minima obtained during the observations to the previous ones, were given. The light curve of the system varies cycle by cycle and the variation is discussed in some extent.