Period and light-curve study of the contact eclipsing binary V523 Cas

CCD photometry of the eclipsing W Uma binary system V523 Cas in U, B, V and R_C filters was carried out during eight nights in 2012. The physical and geometrical parameters of this system are obtained. A possible pulsation period of one of the components is obtained by analyzing the residuals of the ephemeris light curve. Our observations contain 16 times of minimum light. We combined these with all available published times of minimum. By fitting a quadratic curve to the O-C values, a new ephemeris of the system is calculated. By attributing the period change to mass transfer, we find a mass transfer rate of $4\times {10}^{-12}$$\frac{M_{\odot }}{yr}$. Also, Period (80.58 yr) and the minimum mass (0.3 M_⊙) of a possible third body is estimated. In addition, the possible existence of a fourth body with a mass of order 0.15 M_⊙ is discussed. These third and fourth bodies could be low-mass main-sequence stars (red dwarfs).     

The UBVRI photometry and polarimetry of the young binary system V628 Cas

The results of multicolor photopolarimetric observations of the Ae/Be Herbig star V628 Cas are presented. It has been shown that the observed changes of the linear polarization correlate with the phase of the orbital period. The system demonstrated changes in brightness, the amplitude of which decreases from 0.4 to 0.1m when moving from the U band to the I band. No dependence of the polarization degree on the brightness is observed.     

B-V photoelectric photometry of white-dwarf eclipsing binary V471 Tauri

Photoelectric photometry of the unusual binary system, whose light curve shows peculiar light variations, has been done in the two colours. The observations obtained at the Ege University Observatory between 1973 and 1978 and at the Kottamia Observatory in November 1977 show a variable light curve. The observed variations in the light curve show a migrating wave towards a decreasing orbital phase similar to those observed in RS CVn-binaries. The migration period appears to be about 191 days. The times of minima indicate that there has been a decrease on the orbital period of the system. However, since there is not enough material on the observed times of minima, we cannot explain whether the decrease in the orbital period has been sudden or gradual. The radii of the components have been computed from the primary minimum alone. With the available spectroscopic data, the absolute dimensions of the components are also presented. It appears to be difficult to explain the evolution of the system without taking into consideration the mass loss. The proposed models for the evolution of the system and an explanation of the observed light variations are also presented.     

Discovery of a cyclic period change in the contact binary system V1128 Tau

We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components.     

B and V photometry and analysis of the eclipsing binary RZ Cas

Photoelectric light curves of the eclipsing binary RZ Cas are presented forB andV filters. The light curves are analysed for light and geometrical elements, starting with a previously suggested preliminary method. The approximate results thus obtained are then optimised through the Wilson-Devinney computer programs.     

Velocity curve studies of spectroscopic binary stars V380 Cygni, V401 Cyg, V523 Cas, V373 Cas and V2388 Oph

Using measured radial velocity data of five double lined spectroscopic binary systems V380 Cygni, V401 Cyg, V523 Cas, V373 Cas and V2388 Oph, we find corresponding orbital and spectroscopic elements via the method introduced by Karami & Mohebi (2007) and Karami & Teimoorinia (2007). Our numerical results are in good agreement wit. those obtained by others using more traditional methods.     

Early-type W UMa contact binary system: New data on V535 Ara

This paper presents the results of spectroscopic and photometric observations of the early-type W UMa system V535 Ara. New high-resolution spectra were taken at the Mt. John University Observatory in 2007. Radial velocities and spectroscopic orbital elements of the system were determined by applying KOREL spectral disentangling. The resulting orbital elements were: a₁sini = 0.0047 ± 0.0001 AU, a₂sini = 0.0146 ± 0.0001 AU, M₁sin³i = 1.85 ± 0.01 M_⊙, and M₂sin³i = 0.59 ± 0.01 M_⊙. The components were found to be in synchronous rotation following examination of their disentangled Hγ line profiles. Four photometric data-sets (1966 BV, 1967 BV, HIPPARCOS and ASAS) were modeled using the Wilson-Devinney method. The model describes V535 Ara as an A sub-type W UMa type eclipsing binary which has a fill out factor of 0.22 in marginal contact configuration. The simultaneous solution of light and radial velocity curves gave the following absolute parameters: M₁ = 1.94 ± 0.04 M_⊙, M₂ = 0.59 ± 0.02 M_⊙, R₁ = 2.09 ± 0.03 R_⊙, R₂ = 1.23 ± 0.02R_⊙, L₁ = 18 ± 3 L_⊙ and L₂ = 6 ± 1 L_⊙. The distance to V535 Ara was calculated as 123 ± 20 pc using distance modulus with correction for interstellar extinction.     

New findings based on long-term photometric observations of the eclipsing binary V471 Tauri

The post-common envelope and pre-cataclysmic binary V471 Tau has been observed by the authors since 1973. At least a complete light curve in B and V bands and more than two eclipse timings were obtained in each year. All the available data published so far (including the authors') have been collected and analysed for the brightness and orbital period changes. The system brightened about 0.22 mag in both B and V bands more or less regularly up to 1997 and started to decrease afterwards. A search for periodicity of this variation yields a period longer than 85 yr. In addition to this long-period variation, a small amplitude of about 0.08 mag and short time-interval fluctuations on the mean brightness have been detected. The variations of the mean brightness have been discussed and plausible causes suggested. The changes of the apparent period have been attributed to a third body. Analysis of all the 'observed−calculated' (O−C) data yields a period of 32.4 yr, with a semi-amplitude of 151 s and an eccentricity of 0.30 for the third-body orbit. For orbital inclinations greater than 34° the mass of the third body would possibly match to a brown dwarf. One of the most interesting features in the light curve of V471 Tau is the decrement of the eclipse depth with time. The depth of the eclipse in the B band has been decreased from 0.082 to 0.057 mag over 34 yr. Subtracting the variation of the depth due to the brightening of the red dwarf star, the actual variation in depth, originated from from the white dwarf, was found to be about 0.012 mag. This change in the brightness of the compact object has been attributed to the mass accretion from its primary component via thermally driven wind and/or flare-like events.     

Photometric investigation on the W-subtype contact binary V1197 Her

Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney(W-D) program was used to model the observational light curves. The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q = 2.61 and a fill-out factor of f = 15.7%. The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact status.The orbital inclination of V1197 Her is as high as i = 82.7?, and the primary star is completely eclipsed at the primary minimum. The totally eclipsing characteristic implies that the determined physical parameters are highly reliable. The masses, radii and luminosities of the primary star(star 1) and secondary star(star2) are estimated to be M1 = 0.30(1) M_⊙, M2 = 0.77(2) M_⊙, R1 = 0.54(1) R_⊙, R2 = 0.83(1) R_⊙,L1 = 0.18(1) L_⊙and L2 = 0.38(1) L_⊙. The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram, showing that the less massive but hotter primary star is more evolved than the secondary star. The period of V1197 Her is decreasing continuously at a rate of d P/dt =-2.58 ×10-7 day · year-1, which can be explained by mass transfer from the more massive star to the less massive one at a rate of dM_2/dt=-1.61 × 10~(-7) M_⊙year~(-1). The light curves of V1197 Her are reported to show the O'Connell effect. Thus, a cool spot is added to the more massive star to model the asymmetry in the light curves.     

A photometric study of the contact binaries V523 Cas and TY UMa

Broad-band V and I photometry of the short-period W UMa-type contact binaries V523 Cas and TY UMa are reported. From the light curves, the system parameters have been determined and evidence is presented for extensive spot activity in both systems, with V523 Cas being the more active system. A compilation of all the available photoelectric and CCD-based timings of eclipse minima is made; the O–C diagrams show evidence for an increasing period in the case of V523 Cas and a decreasing period in TY UMa. In addition we derive a more accurate astrometric position for V523 Cas from our CCD images.     

The contact binary system YY Eri

Relatively new and unanalysed photometric data-sets of the contact binary system YY Eri are presented. The light curves have been analysed using information limit optimization techniques, and the Binary Maker program of Bradstreet (1992).Comparison of the results allows insight into determinacy questions affecting the W UMa type of light curve, which relates to our general understanding of contact binaries. A limiting contact configuration cannot be ruled out on the basis of empirical data-analysis alone.Very careful analysis of the photospheric flux distribution over the surface of the Sun may help establish appropriate values of the gravity brightening parameter for cool dwarf stars. At present, however, empirical photometric information on contact binaries is non-discriminatory: i.e. alternative cosmogonies can find alternative support from available evidence. The implication is then for more and better observational data to allow better real independent parameter determination.     

Analysis of the V light curve of the system CW Cas

The V light curve of CW Cas, observed during 1972, has been analysed by different methods of solution. The results show great differences between rectifiable and direct methods.     

Spot patterns and differential rotation in the eclipsing pre-cataclysmic variable binary, V471 Tau

We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high-latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system. Our results reveal that the star is rotating rigidly with a surface shear rate,  dΩ= 1.6 ± 6 mrad d⁻¹  . The single active star AB Dor has a similar spectral type, rotation period and activity level as the K star in V471 Tau, but displays much stronger surface shear  (46 < dΩ < 58 mrad d⁻¹)  . Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs.