KR Cygni: a near-contact eclipsing binary?

In this study we present photometric observations of the eclipsing binary KR Cyg made in 1999 and 2000. The observations of the eclipsing binary KR Cyg have been carried out in B, V and R colours at the Ege University Observatory. A new seasonal light curves are presented. New times of minima and ephemerides are given. Based on a statistical analysis of the times of minima obtained by photoelectric photometry, the orbital period of the system is found to be constant. The photometric mass ratio of the system is well determined. The corresponding light curves were analyzed by the Wilson-Devinney code. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared and visible photometry of the RS CVn-star II peg

Infrared photometry inJ. H, K, L, M bands carried out in different years from 1983 to 1986, andU, B, V, R, I quasi-simultaneous to 1984 are presented.Although the amplitude of the minima decrease as the wavelength increase, the infrared light curves show a similar behaviour to that observed in visible.Since no variations in the average magnitudes are notted from 1983 to 1986, we could assumed that the activity of II Peg is not increasing. Also from the light curves a concentration process of the spots seems to have taken place from 1984 to 1986.In the analysis of the infrared colours an excess attributable to circumstellar dust emission is found.     

U,B, V light curves of CO Lacertae

CO Lacertae is one of the very few known binaries with both a short period of apsidal motion and good M, L, R data. Our newU, B, V light curves provide two times of minima and a check on Semeniuk's value forP _aps. This is the first published example of an eclipsing binary analysed in terms of a physical model (as opposed to a model based on spherical or ellipsoidal star figures) which allows for eccentric orbit effects. The light curves show some peculiarities — particularly a large, probably intrinsic, scatter.     

Period variation and spot model for the W UMa type binary TY UMa

We present the full VRI light curves and the times of minima of TY UMa to provide a complete photometric solution and a long-term trend of period variation. The light curves show a high degree of asymmetry (the O'Connell effect). The maxima at 0.25 phase (Max I) are 0.021, 0.015, and 0.020 mag fainter than those at 0.75 phase (Max II) in V , R , and I , respectively. The period of TY UMa has varied in a sinusoidal way, superimposed on the long-term upward parabolic variation. The secularly increasing rate of the period is deduced as 1.83 s per century  ( P˙ / P =5.788×10^-10 d d^-1)  . The period of sinusoidal variation is about 57.4 yr. The spot model has been applied to fit the asymmetric light curves of TY UMa, to explain light variations. By changing only the spot parameters, the model light curves can fit the observed light curves for three epochs. This indicates that the variation of the spot location and size is the main reason for changing the shape of light curves, including two different maxima and the interchanging depths of occultation and transit minima.     

A study of the distortion wave in the RS CVn eclipsing binary SV Camelopardalis

The light outside the eclipses of the totally eclipsing RS CVn binary SV Camelopardalis (SV Cam) is Fourier analysed and the amplitudes of the distortion waves have been derived. The distribution of the percentage contributions of these amplitudes inV, B andU colours with respect to the luminosities of the binary components indicates that the hotter component is the source of the distortion waves. These distortion waves, attributed to star spots, are modelled according to Budding (1977) and spot parameters like longitude, latitude, temperature and size are obtained. From this study it is noticed that while symmetric waves with two minima could be fitted satisfactorily, asymmetric waves with more than two minima could not be fitted well. From the longitudes of the minima of the best fitted curves, migration periods of four spot groups are determined. Assuming synchronism between rotation and orbital periods, the rotation periods of the four spot groups are derived from their migration periods. The period of rotation of one of the spot groups having direct motion is found to be 0^d.5934209 while the periods of the other three spot groups having retrograde motion are 0^d.5926588, 0^d.592607 and 0^d.5924688. As the latitudes of these spots are known from modelling parameters, the latitude having a rotation period equal to that of the orbital period (co-rotating latitude) is found to be about 30°     

The distortions in the light curves of MM herculis

The RS CVn-type eclipsing binary MM Her was observed photoelectrically inB andV colours. The light curves obtained in 1984 and 1985 are presented. It was found that the depths of the primary minima are decreased from 1983 to 1985. However, the amplitude of the wave-like distortion outside the eclipses was detected to increase since 1976. The period of migration was determined to be about 3.57±0.08 years.     

Charge-coupled device observations of V388 Cyg

We present BVR full-light curves of V388 Cyg to provide a complete photometric solution for the first time. The light curves show a high degree of asymmetry (O'Connell effect). The maxima at 0.25 phase (Max I) are 0.023, 0.018 and 0.012 mag higher than those at 0.75 phase (Max II) in B , V and R , respectively. Three possible spot models are applied to fit the asymmetric light curves of V388 Cyg, in order to explain the O'Connell effect. We conclude that the model of the cool spot on the cooler star is the most reasonable model for V388 Cyg. The continuous period variation is confirmed by recently collected times of minima, including one minimum that is determined in this paper. The period decrease rate is estimated as d p /d t =−2.055×10⁻⁷ d yr⁻¹ .     

Light curve variations of the eclipsing binary V367 Cygni

The long-period eclipsing binary star V367 Cygni has been observed photoelectrically in two colours,B andV, in 1984, 1985, and 1986. These new light curves of the system have been discussed and compared for the light-variability with the earlier ones presented by Heiser (1962). Using some of the previously published photoelectric light curves and the present ones, several primary minima times have been derived to calculate the light elements. Any attempt to obtain a photometric solution of the binary is so complicated by the peculiar nature of the light curve caused by the presence of the circumstellar matter in the system. Despite this difficulty, however, some approaches are being carried out to solve the light curves which will be discussed shortly.     

Das System des Bedeckungssterns TT Lyrae

For this typical Algol system with the period 5.24 days, complete light curves in two colours have been derived from 160 photoelectric measurements in B and 173 in V. The primary minimum has been found to be total and asymmetric. To get a satisfactory photometric solution it was necessary to allow for the dissimilarity of the components. For the coefficients of limbdarkening of the Ao-component the values x = 0.35 · 0.11 (B) and 0.44 · 0.10 (V) have been deduced.     

Photoelectric photometry of the eclipsing binary MM herculis: Preliminary results

The RS CVn-type eclipsing binary star MM Her has been observed in two colours,B andV, in 1979, 1980, and 1983. Several minima times were obtained during the observations and new light elements calculated. The light curves of the system obtained in blue and yellow lights show a significant wave-like distortion which migrates towards the decreasing orbital phases. Its migration period was estimated to be about 3.5 yr. The amplitudes of the wave-like distortion inB andV appear to change each year. The primary minimum of the system is a total eclipse with a duration of 0^d.08.     

A photometric light variation and a 1500 days secondary period in the W UMa system TZ bootis

Photoelectric observations of the eclipsing variable TZ Bootis, obtained in 1983 and 1986, in the two coloursB andV are presented: They are compared with the previous light curves of the system. The light curve changes show that the system TZ Bootis has a solar-like activity cycle with a period of 1500 days. The primary shows a transit, whereas the secondary shows an occultation minima. The maxima exhibit a large difference suggesting a large complication in the system. The (O-C) trend indicates that the period did not remain constant; a satisfactory representation of all the observed time of minimum light was obtaiend assuming a linear trend in the (O-C)s. The star may be classified to A-type W UMa systems.     

Light curve variation and period changes of VW Cep

PhotometricUBV-observations of VW Cep, a W UMa-type eclipsing binary, were made in 1971 and 1978–79. The (O-C)-diagram, with the newly determined times of minima extended, shows sudden increases and decreases in the period of VW Cep. The difference light curves (the observed light curves compared with a reference light curve) show some correlations with the sudden change of the period. In particular, the difference between the two light curves from 1971 and 1978 is also presented. The system may be in marginal contact, and as such is possibly unstable with respect to mass exchange between its components. In accordance with the variation of (O-C)-values the mass transfer between the both components is discussed. The difference between the depths of the two minima shows irregular changes, while that between the heights of the two maxima shows a long term variation on which irregular fluctuations are superimposed.     

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 42 ^m .5.     

Light variation of the variable star OO Aquilae

PhotoelectricB andV observations of the W UMa-type system OO Aql have been obtained for 11 nights during the period from 22 June–30 July, 1987. A total of 978 observations were obtained in eachB andV filter. All these observations were transformed to theB andV colours of theUBV standard system. Five light curves for primary and secondary eclipses were obtained, its times of minima were determined and a new linear ephemeris was given. The period changes of the system were discussed.     

New times of the minima and light elements of SW Lacertae

SW Lacertae is a short-period variable star of the W UMa-type. A total of 261 photoelectric observations for eachU, B, andV filter were obtained in 1986 while 522 photoelectric observations for eachB andV filter were obtained in 1987. All these observations were transformed to theU, B, andV colours of theUBV standard system. Nine light curves for primary and secondary eclipses were obtained, their times of minima were determined and a new linear ephemeris was obtained. The period changes of the system were also discussed.     

First photometric analysis of the two EW binaries ZTF J214226.88+435827.1 and KAO-EGYPT J214216.38+440015.1

The EW-type eclipsing binaries are strongly interacting systems known to have often both component stars filling their crucial Roche lobes and having a common envelope. We present new BVRI light curves of the eclipsing binaries ZTF J214226.88+435,827.1 (ZTF21+43) and KAO-EGYPT J214216.38+440,015.1 (KAO21+44) based on CCD observations acquired with the 1.88-m Kottamia Astronomical Observatory (KAO) at Newtonian and Cassegrain telescope focus. The modeling results show that these two systems are to be W UMa contact binaries belonging to EW subtypes. All the light curves show the inverse O'Connell effect. We computed new ephemeris for each system using our times of minima and that available in the literature. Using our new times of minima and epochs for both systems from all available observations, the orbital period changes of these structures are studied for our systems. Using the PHOEBE package, a preliminary determination of the two systems' photometric orbital and physical parameters has been present. The positions of the systems were also depicted on the Hertzsprung-Russell (H-R), M-L, and T_eff-L diagrams to test their evolutionary status.     

The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U - B, B - V, V-R and V-I colours and absorption-line indices denned by the Lick Observatory image dissector scanner (referred to as Lick/IDS), for instantaneous burst solarmetallicity single stellar populations with ages in the range 1-15 Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U - B and B - V colours obtained by the two methods agree with one another, while the V - R and V - I colours by the traditional method are bluer than those by Monte Carlo simulation. A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO1 and TiO2 are consistent with those for the Monte Carlo simulation.     

Photovisual light curve and photometric elements of the eclipsing nucleus of the planetary nebula Abell 63

The firstV-photoelectric light curve (on theUBV system) of the eclipsing variable UU Sagittae (constituting the central star of a faint planetary nebula Abell 63) was obtained in 1979 with the 74 in. reflector at the Kottamia station of Helwan Observatory in Egypt, and analysed for the photometric elements of the system. Some of the geometrical elements obtained by us differ significantly from those previously deduced by Bondet al. (1978) from theirB-light curve secured in 1976; but there is no reason to suspect from this that any physical change has taken place in the system between 1976 and 1979.The most significant feature of the light curve of UU Sge (in both colours) is the large amplitude of the reflection effect exhibited between minima, as well as the fact that the secondary minimum appears to be almost wholly due to an eclipse of reflected light. This, combined with the depths of the alternate minima observed in both colours, leads us to conclude that the effective temperature of the O-type component is probably not much higher than 30 000 K, while that of the secondary component is not less than 6000 K (corresponding to a subgiant of spectral class close to G0).     

Remarks on erratic period fluctuations of detached close binaries and the constancy of the orbital period of XY UMa

It is shown that the erratic changes of the orbital period, which are observed in some detached eclipsing binary systems, cannot be interpreted as real if their light curves show changing anomalies with asymmetric minimum profiles. In this case the photometrically determined times of the minima do not coincide with the ideal geometric ones, which are unobservable. This fact and the applied reduction methods for deriving the photometric times of minima cause systematic period errors of cumulative character. The discussion of six photoelectrically-determined minima obtained within the last 20 yr, and earlier photographic ones of the 0^d.479 period eclipsing binary XY UMa yields a constant period. The long cyclic light curve variations due to starspot activity of the larger and hotter component of this system are reflected in corresponding period oscillations. Dedicated to Dr. Ida Noddack on the occasion of her eightieth birthday.     

Light variations of RT Lac during the last ten years

The RS CVn-type eclipsing binary star RT Lac has been observed inB andV colours, during 1984, 1985, 1986, 1987, and 1988 observing seasons. The orbital period of the system was found to be decreasing with an amount of 62 s century^–1. The brightnesses both at minima and maxima are changing with time. It seems that the variations of the brightnesses at mid-primary and second quarter are similar, but at second first quarters are opposite to each other. We believe that these variations are mainly related with the spots (or spot groups) located on the surface of the component star which is in front during the primary minimum. We also estimate the period of the spot activity cycle to be approximately six years.