W UMa-type stars BV Dra conis and BW DRa conis: Photoelectric observations

Photoelectric UBV observations of two W UMa-type stars, BV Dra (ADS 9537A) and BW Dra (ADS 9537B), are presented. New periods and epochs of minima are given for both variables, and magnitudes at maximum light are determined from standard star observations. It is concluded that these variables are quite normal W UMa stars.The two variables are members of the visual binary star ADS 9537, for which the angular separation and the position angle are determined from the photographic observations.On leave of absence from Dept. of Earth Science and Astronomy, College of General Education University of Tokyo.     

O'Connell effect in early‐type contact binaries: DU Boo and AG Vir

The paper presents new photoelectric observations of the eclipsing binary systems DU Boo and AG Vir. The systems are somewhat similar – both are A‐type contact binaries with the maximum following the primary minimum being the brighter one. This light curve asymmetry is extremely temporally stable. The phase dependence of the color indices is unexpectedly small for the observed amplitude of the O'Connell effect, amounting to about 0.1 mag in the optical wavelength range which indicates a very large heated area with a temperature contrast of ΔT ≈ 1000–1500 K. The broadening functions (BFs) of the systems do not show any dark solar‐type photospheric spots. On the other hand, there are significant differences of BFs between the quadratures (surprisingly similar in both systems) indicative of stream of matter or bright region causing additional emission seen between the components around the phase 0.25. Absolute parameters of the components slightly depend on the adopted model. Long orbital period of both contact binaries combined with late spectral type indicate that the primary components of either of the systems (but particularly in case of DU Boo) already evolved off the main sequence (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations into the thermal non-equilibrium of W UMa-type contact binaries

Traditionally, some physical details(e.g., magnetic braking, energy transfer, angular momentum loss, etc.) have to be taken into consideration during investigations into the evolution of contact binaries. However, the real evolutionary processes which usually contain several of these physical mechanisms are very complicated as a result of strong interaction between components. To avoid dealing with these factors, a linear relationship is applied to the temperatures of components. It is found that the higher the mass ratio(M_2/M_1) of a contact system, the weaker the deviation from thermal equilibrium.On this basis, a variation trend of fill-out factor(f) changing with mass ratio can be inferred, which is consistent with observations. Moreover, if we stick to this point of view, it should be natural that the number of semi-detached binaries in the predicted broken-contact phase of relaxation oscillations is less than the number in the contact phase.     

Possible solution to the problem of the extreme mass ratio W UMa-type binaries

When the total angular momentum of a binary system is at a critical (minimum) value, a tidal instability occurs (Darwin's instability), eventually forcing the stars to merge into a single, rapidly rotating object. The instability sets in at some critical separation which in the case of contact binaries corresponds to a minimum mass ratio depending on dimensionless gyration radius k ₁. If one considers   n = 3  polytrope (fully radiative primary with  Γ₁= 4/3  ),   k ²₁= 0.075  and   q _min≈ 0.085–0.095  . There appears to be, however, some W UMa-type binaries with q values very close, if not below these theoretical limits, implying that primary in these systems is probably more centrally condensed. We try to solve the discrepancy between theory and observations by considering rotating polytropes. We show by deriving and solving a modified Lane–Emden equation for   n = 3  polytrope that including the effects of rotation does increase the central concentration and could reduce   q _min  to as low as 0.070–0.074, more consistent with the observed population.     

An observational study of a spotted W UMa-type binary star CK Bootis

New photoelectric observations of CK Bootis (a binary star suspected of a spot activity) obtained in 1988 at Mt. Suhora Observatory are presented. On the basis of the spectroscopic observations made in May 1990 at the Toru University Observatory the spectral class F6V of the primary component was estimated. The physical parameters of the system with a circular spot were derived making use of the Wilson-Devinney code.     

Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.     

CCD photometry of W UMa-type contact binaries in the old open cluster Berkeley 39

We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39.The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India.The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented.The light curves appear to be symmetric in all the passbands.The photometric solutions suggest that the variables are W-type systems.The new ephemeris ind...     

New observations,photometric study and preliminary elements of the W UMa system DF CVn

CCD (V) light curve of the EW‐type eclipsing variable DF CVn was obtained during seven nights in April–May, 2004. With our data we were able to determine 4 new times of minimum light. The light curve appears to exhibit a typical O'Connell effect, with Maximum I brighter than Maximum II by 0.013 mag. in V. TwoWilson‐Devinney (WD) code working sessions, using the V light curve, were done with and without spots. The analysis of the results shows that the best fit was obtained with the spotted solution and indicates contact geometry. The photometric mass ratio of the system is found to be q = 0.347 and its inclination i = 72°, the primary minimum shows a transit. The star may be classified as an A‐type W Uma system. Assuming a reasonable value for the mass of the primary component an estimate of the absolute elements of DF CVn has been made, with the assumption that the primary has a mass corresponding to its spectral type according to Straizys and Kuriliene (1981). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometry of δSct—type and Related Stars：Results of AD Ari,IP Vir and YZ Boo

Photometric results of three δ Scuti stars, AD Ari,IP Vir and YZ Boo from new observations obtained at the Xinglong Station of the Beijing Astronomical Observatory (BAO) during 2000 and 2001 are reported. We present here the preliminary analyses. Detailed studies of these stars based on additional data will be published separately.     

Photometric investigation and orbital period analyses of the W UMa binaries FP Lyn,FV CVn and V354 UMa

New light curves and photometric solutions of FP Lyn, FV CVn and V354 UMa are presented.We found that these three systems are W-subtype shallow contact binaries. In addition, it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric. Therefore, a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa. At the same time, we added a third light to the photometric solution of FP Lyn for the final result. The obtained mass ratios and fill-out factors are q = 1.153 and f = 13.4% for FP Lyn, q = 1.075 and f = 4.6% for FV CVn, and q = 3.623 and f = 10.7% for V354 UMa respectively. The investigations of orbital period for these three systems indicate that the periods are variable. FP Lyn and V354 UMa were discovered to have secularly increasing components with rates of dp/dt = 4.19 × 10~(-7) d yr~(-1) and dp/dt = 7.70 × 10~(-7) d yr~(-1) respectively,which are feasibly caused by conservative mass transfer from the less massive component to the more massive component. In addition, some variable components were discovered for FV CVn, including a rate of dp/dt =~(-1).13 × 10~(-6) d yr~(-1) accompanied by a cyclic oscillation with amplitude and period of 0.0069 d and 10.65 yr respectively. The most likely explanation for the long-term decrease is angular momentum loss.The existence of an additional star is the most plausible explanation for the periodic variation.     

New photoelectric observations and elements of the eclipsing W UMa-type system V839 Oph

The W UMa-type system V839 Oph was observed photoelectrically in two wavebands (B andV) during 1985 at the Kryonerion Astronomical Station of the National Observatory of Greece. The light curves of the system are analysed using the frequency-domain techniques and new geometric and photometric elements are given. The light variations of the system are also discussed.     

Rotational measurement and study of RS CVn binaries. II

For 37 components belonging to 31 RS CVn binary systems, we measured the rotation using Reticon data on the 2.1 McDonald Reflector. Combining our previous data for 38 components, we made a statistical analysis on the question of synchronous rotation. Our results show that, while the great majority show synchronous rotation, exceptions are found in all period groups, contradicting the generally held view that all short period and normal period RS CVn stars have synchronous rotation and all long period ones do not.     

The W UMa-type Stars Program: First Results, Current Status and Perspectives

We present the results of a statistical investigation of the period-color and period-bolometric magnitude relations using a carefully selected sample of 120 contact systems with known physical parameters.     

Reanalysis of the orbital period variations of two DLMR overcontact binaries:FG Hya and GR Vir

We investigate orbital period changes of two deep, low mass ratio(DLMR) overcontact W UMa-type binaries, FG Hya and GR Vir. It is found that the orbital period of FG Hya shows a cyclic change with a period of P_(mod)= 54.44 yr. The cyclic oscillation may be due to a third body in an eccentric orbit, while the orbital period of GR Vir shows a periodic variation with a period of P_(mod)= 28.56 yr and an amplitude of A = 0.0352 d. The periodic variation of GR Vir can be interpreted as a result of either the light-time effect of an unseen third body or the magnetic activity cycle.     

Evolutionary status of UV Piscium and its comparison with other short period RS CVn binaries

From the derived elements of UV Piscium, the evolutionary status of both of its components are compared with the Schaller et al. models and also with other main sequence systems having spectral types of late F to K range. From these models the ages of the components of UV Psc are determined. The Rossby number, which is a measure of chromospheric activity, has been derived from the convective turnover time scales and also from the age estimates.     

Physical parameters of some close binaries: ET Boo,V1123 Tau,V1191 Cyg,V1073 Cyg and V357 Peg

With the aim of providing new and up-to-date absolute parameters of some close binary systems, new BVR CCD photometry was carried out at the Ankara University Observatory (AUG) for five eclipsing binaries, ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In this paper, we present the orbital solutions for these systems obtained by simultaneous light and radial velocity curve analyses. Extensive orbital solution and absolute parameters for ET Boo system were given for the first time through this study. According to the analyses, ET Boo is a detached binary while the parameters of four remaining systems are consistent with the nature of contact binaries. The evolutionary status of the components of these systems are also discussed by referring to their absolute parameters found in this study.     

Imaging the cool stars in the interacting binaries AE Aqr,BV Cen and V426 Oph

It is well known that magnetic activity in late‐type stars increases with increasing rotation rate. Using inversion techniques akin to medical imaging, the rotationally broadened profiles from such stars can be used to reconstruct ‘Doppler images’ of the distribution of cool, dark starspots on their stellar surfaces. Interacting binaries, however, contain some of the most rapidly rotating late‐type stars known and thus provide important tests of stellar dynamo models. Furthermore, magnetic activity is thought to play a key role in their evolution, behaviour and accretion dynamics. Despite this, we know comparatively little about the magnetic activity and its influence on such binaries. In this review we summarise the concepts behind indirect imaging of these systems, and present movies of the starspot distributions on the cool stars in some interacting binaries. We conclude with a look at the future opportunities that such studies may provide. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

BV and narrow-band observations of the eclipsing binary AM Leonis

Photometric observations obtained between 1977 and 1981 are reported. The period of AM Leo did not change during the last 20 years. Light curve variability was found to affect prominently the depths and shapes of the minima. The effects of the complications on broad and narrow band colour indices are discussed. Because of the complications element determinations of AM Leo seem to be reliable only with restrictions.